All stamps are not the same. There are rare stamps. There are common stamps. There are gems. There are space fillers. And in between all of that is a huge array of varying conditions and values. Unfortunately, the Scott catalog is only provides prices for stamps that are with VF centering and without faults. The Scott Valuing Supplement provides a breakdown with various degrees of centering. No catalog that I know of tries to price stamps with faults, etc.
What I'm giving you here are the retail price structures as I see them. Not every dealer may agree with my analysis. So don't take this as written in stone. What I hope you will get out of it is a reasonable estimate of what something is worth. There will be exceptions to the guidelines I'm laying out here. Every stamp doesn't fit the mold perfectly and that's OK. What I'm giving you here will fit most stamps, but not every single stamp.
I'm going to use terms like tiny, small, and large. Not everyone has the same perception of what those terms mean. What is tiny to one person may not be tiny to someone else. My definition of tiny is something about the size of a pin head or less. In other words, you have to look close to really see it. Small is something more like the size of 2 or 3 pin heads. It's noticeable, but it's not horrible. After that, you start talking about things that are large or affect the percentage of the whole stamp, e.g., 25% disturbed gum and so forth.
The first topic is centering. The Scott catalog values are for Very Fine (VF) centered stamps. The Scott Valuing Supplement goes into a breakdown based on more degrees of centering. Here is how I view centering and how I price stamps. I won't rehash my arguments about stamp grading and the astronomical prices some modern copies bring at auction.
Gem or Superb stamps are the best you can buy. Under 30x magnification, they have perfectly even margins. Stamps like these are rarely encountered. Stamps like this bring anywhere from 2-10 times catalog value depending on scarcity of the issue. For example, Scott #300 is common so a Gem stamp is more likely to go in the smaller multiple of catalog value range. But Scott #245 is a scarce stamp and a Gem copy will sell for several multiples of catalog value.
Extra Fine (XF) stamps are seldom encountered. Appearance to the unaided eye may look like a Gem stamp. But under 30x magnification, there is a slight difference in margin sizes between the edge of the stamp design and the perforation holes. Stamps like these bring more in the 2-5 times catalog value range.
Very Fine (VF) stamps are well centered. If you look at it with the naked eye, you can tell that the stamp is off center to one or two sides. The stamp design is well clear of the perforations. This is what the Scott catalog uses as a basis for its prices. Stamps like these sell for around catalog value.
Fine to Very Fine (F-VF) stamps are noticeably off center on one or two sides. However, the stamp design is clear of the perforations. There is some white space between the edges of the perforations and the edge of the stamp design. Stamps like these sell for around 50-70% of catalog value depending on the scarcity of the issue.
Fine (F) stamps are off center and the perforation holes are extremely close to the edge of the stamp design or they just graze the edge of the stamp design. There is little or no white space between the edge of the stamp design and the edge of the perforation holes. Stamp like this sell in the 25-40% range of catalog value.
Average (AVE) or Very Good (VG) stamps are very off center. The perforation holes cut into the stamp design. There is no white space on the tips of the perforations or only a tiny white space on the tips of the perforations. Stamps like this sell in the 10-20% of catalog value range.
One final note about centering. Sometimes you'll see descriptions like "VF for this issue". I don't believe in describing stamps like that because I think it's confusing. Some stamp issues like Scott #330 are notoriously off center. Using my definitions, you almost never see a VF or better copy on the market. A dealer may take a F-VF copy by my definition and sell it as "VF for this issue" meaning that it's one of the better centered copies you're likely to find.
Don't be fooled by these descriptions. The Scott catalog values are for VF centering unless stated otherwise. Yes, there are a few rare stamps listed in the catalog where all of the known specimens may have less than VF centering. Scott adds a special footnote stating that their catalog price is for such an off center copy.
Not every dealer uses these same definitions for centering. Your best bet is to examine the stamps themselves and decide for yourself if it's F, F-VF, or VF in your own terms. Then purchase accordingly. There are no universally accepted standards in identifying the centering of stamps. It's a subjective process. The grading of stamps is moving us in the direction of an accepted standard for centering, but we're not there yet.
The next topic is gum. Stamps up to about 1870 usually don't have any gum. Year ago, collectors realized that the gum may turn yellow, crack, or damage the stamp. They would soak the gum off to preserve the stamp. You may find some more common stamps (e.g., Scott #11, 24, or 26) that have some gum left. Most unused stamps up to about 1870 are not going to have any gum. The Scott catalog prices them that way.
What if you find an early stamp that has gum? The first thing I would do is have it certified. That adds value to it. Assuming your stamp is not regummed, a hinged stamp with most of the original gum will sell for about 2-5 times catalog value of a no gum copy. A never hinged copy is going to sell for 5-10 times catalog value and quite possibly more because never hinged copies are almost unheard of. A stamp with some original gum but heavily disturbed or hinged will sell more in the 2 times value range while a never hinged copy will sell in the 10 times range or more.
If a stamp from this period has gum, realize that the gum is probably going to be discolored due to age. Manufacturers were concerned about gum that sticks to letters and not about gum that stays fresh for a very long time. The gum may also discolor or stain the face of the stamp. You aren't going to find pristine, never hinged copies with perfect gum and no faults whatsoever on very early US stamps. Such stamps just don't exist.
From 1870 to 1900, most stamps are hinged. You'll find some common stamps like Scott #230 (1¢ Columbian) that are never hinged. Stamps without gum usually sell for about 50% of catalog value for a lightly hinged copy.
From 1900 to 1940, stamps are mixed between hinged and never hinged copies. This is when gum started to become more important and collectors started seeking out never hinged copies. Lightly hinged copies sell for about 30-50% of catalog value compared to never hinged copies. Copies without gum sell for 20-50% of catalog value compared to lightly hinged copies.
After 1940, stamps should be never hinged. A few stamps like the $5 Presidential (Scott #832) and the $5 Hamilton (Scott #1053) are scarce enough that there is a limited demand for lightly hinged copies of those few stamps. Hinged copies after 1940 sell for discount postage. There are too many never hinged copies available at affordable prices. Demand for hinged copies of common stamps is almost non-existent.
The next topic is hinging. The Scott catalog values are for lightly hinged stamps. That is, you can see the hinge mark or there might be tiny pieces of the hinge left behind. But most of the gum is not obscured by the hinge.
Peelable hinges have only been around for a few decades. Back in the 1930s and before, hinges were not so peelable. In fact, removing some old hinges may even damage or thin the stamp if not done carefully. You may encounter such stubborn hinges on early US hinges.
A lightly hinged stamp will sell for close to catalog value or more, depending on the amount of hinging. In some cases, the hinging is extremely light or only affects a very tiny area of the stamp. Those copies usually sell for more than catalog value, but less than a never hinged copy. When a large area of the stamp shows a hinge mark or a few tiny pieces of the old hinge remain, those stamps will sell for around catalog value.
A hinged stamp is one that has a moderate amount of the hinge left behind, typically the moistened part that is stuck to the back of the stamp. Or if the hinge has been removed, the hinged area may be missing some small areas of gum or the gum left behind is lightly disturbed. If the hinge area isn't too big, such copies will sell for 60% or more of catalog value.
Sometimes you will find stamps that have a huge area of hinging or the stamp may have been hinged multiple times. These stamps may have only a small area of undisturbed original gum left. There may be one or more large pieces of hinges left. Stamps like these that have large hinge remnants left behind with very little undisturbed areas of gum are considered heavily hinged. These stamps sell for 50% or less of catalog value of a lightly hinged copy. In some cases, such heavily hinged stamps sell more like a stamp with no gum.
Stamps also come with disturbed gum. The disturbance can come from a variety of sources such as improper storage where the stamp sweats due to the humidity and the gum gets a glazed or glassy appearance. A drop of moisture (water, coffee, soda pop, etc) may have dropped on the gum. Disturbed gum is described in terms of the percentage of the stamp it affects. There are tiny and small disturbed gum areas. Because the effected area is so small, those stamps sell for about the same price as a lightly hinged stamp. Beyond that, disturbed gum is described as 10%, 25%, 50%, and so forth in size. Stamps like that sell for more than copies with no gum, but for less than lightly hinged copies. A range would be between 50% and 90% of the value of a lightly hinged stamp. The more extensive the disturbed gum, the more towards the no gum value the price is going to creep.
Next is faults. Faults come in two categories. There are natural faults. There are faults after the fact.
Natural faults are things like straight edges, paper inclusions and gum skips.
A straight edge stamp will sell for about 50% of a copy with perforations all around. Even through straight edge copies are more scarce, collectors feel that their beauty is diminished by having one or more sides without perforations. Some stamps like coils and booklet stamps only come with a straight edge. But for those stamps where fully perforated copies are available, figure about 50% of the value for a straight edge copies.
Inclusions are tiny disturbances in the paper. The paper making process isn't perfect and sometimes small dust or dirt particles may become embedded in the paper. Or there may be a small dimple in the gum. Such inclusions are usually tiny or small in appearance. But they can decrease the value of the stamp to 50-90% of catalog value compared to a damaged stamp.
Natural gum skips are a common occurrence on early US stamps. Stamps were printed and then gummed before perforating. During the process of applying the gum, sometimes tiny areas of the sheet of stamps were missed. This is especially true in the edges of the gum in the selvedge areas of the sheets or on the outer rows of stamps. For a variety of reasons, these small ungummed areas do appear on stamps before 1940.
A stamp that is never hinged, but it has a natural gum skip will sell for a value that is at or slightly above a copy that is lightly hinged. Many collectors view a gum skip as the same as a hinge mark. The gum isn't perfect and they won't pay the higher price. Gum skips in the margin area generally don't affect the price of never hinged stamps. However, gum skips may affect the price of plate blocks. On some issues, there are very few plate blocks known and tiny natural gum skips are almost considered normal and there is no price difference. On more common stamps (e.g., Scott #632), there is a large supply of plate blocks and there are many copies without gum skips. So a plate block of #632 with a gum skip will sell more at the price of a lightly hinged plate blocks.
Over time, some stamps develop faults – usually through improper storage or handling. The price of the stamp depends on how large and how noticeable the fault is.
Some stamps have faults, but they are still attractive. These are stamps that have light creases, tiny or small thin areas. From the front, the stamp may appear normal. These stamps sell for 50% or more of catalog value compared to an undamaged stamp with the same centering. The smaller the fault, the more towards full catalog value an item is worth. The larger the fault, the less it will sell for.
Some stamps have small to moderate faults. They are not quite as attractive. These stamps have larger thin areas. A few of the perforations may be trimmed off or very blunt or quite ragged. They may have a pin hole. While still attractive, something tends to stand out about their appearance like the pin hole or the ragged perforations. Stamps like this sell more for 20-50% of catalog value. Again, the more noticeable the damage, the less it will sell for.
Some stamps have major problems. They are heavily creased. They have large areas that are thinned. They may be missing corners or pieces of the stamp. The stamp may be cut in half and only held together with a hinge. When you see them, they stick out like a sore thumb. These are often called seconds or space fillers. These stamps typically sell in the 2-20% range of catalog value. If a stamp has a huge thin and it's not noticeable from the front, then 10-20% may be more appropriate since it is still somewhat attractive looking. A stamp with a missing piece is going to sell more in the 2-10% range depending on how much is missing.
Another "fault" is stamps with markings on the back. It past years, it was common for dealers or philatelic experts to lightly stamp the back of a stamp with a tiny, indelible mark. This is called an expertizing mark. It was to symbolize that the stamp was authentic as to its catalog number. Also, some collectors would use pen or pencil and mark the Scott catalog number on the reverse side of a stamp. On used stamps, these marks are small and unobtrusive. On mint stamps, the marks do detract from the pristine condition of the gum.
Expert marks are a difficult area to price. For used stamps, any decrease in value is small. Stamps like this usually sell for 75% or more of catalog value. In the cases where a famous philatelist placed his mark on the back of a stamp, the stamp may sell for more than catalog value because someone is willing to pay a premium to own a stamp once owned or examined by a famous philatelist or dealer from the past.
On mint stamps, an expert mark makes the stamp slightly damaged. It's no longer pristine, never hinged gum. If the stamp is hinged, an expert mark won't affect the price much at all, perhaps 75-90% of the retail value. If the stamp is never hinged, the mark may reduce the price to as much as 50% of the retail value. Again, some stamp may sell for more than catalog value if expertized by a famous philatelist or dealer.
Most of the post-1940 material is very common. Damaged stamps don't sell at all. If they are used, give them to kids to get them started in stamps. If they are really damaged, like stuck down with scotch tape, you're probably better off throwing them away if they don't have any sentimental value. If they are mint, use them up for postage. Undamaged copies of post-1940 material are too plentiful and very affordable.
On stamps before 1940, there is very limited demand for damaged stamps that catalog $20 or under in value. For very common stamps like Scott #300, damaged used stamps are worthless. There are too many good copies available at affordable prices. Most collectors can afford $20 or less for a stamp. Damaged copies in this range usually don't sell for more than 50% of catalog value. Heavily damaged copies don't sell well at all at any price.
For stamps in the $20-100 range, a market for damaged copies emerges. These stamps begin to go beyond the budgets of average stamp collectors. Lightly damaged stamps sell OK. Heavily damaged stamps are questionable.
For stamps in the $100-$500 range, the market for damaged copies is stronger. Lightly damaged stamps sell well. Heavily damaged stamps sell too, but more in the 2-10% range of catalog value.
For stamps over $500 in catalog value, there is a market for damaged material. Lightly damaged material sells well. Collectors who want attractive stamps but they don't have the budget to spend that much money for a single stamp like this kind of material. They fill holes in their albums at affordable prices and the collection still looks nice from the front. Heavily damaged stamps sell OK for collectors looking to fill spaces in their albums at bargain prices.
The opposite of faults are things that bring a premium. For example, margin copies with selvedge attached, plate number singles, margin copies with various plate markings, plate varieties, and so forth.
Sometimes the stamp is immaterial in determining value. For example, suppose you had a sheet of stamps that was signed by Postmaster General James Farley. It doesn't matter much whether he signed a sheet of Scott #743 or Scott #744. The big factor in determining the value is in the autograph. If you're interested in things like that, I suggest you seek out information in those respective fields. There are too many things like autographs that add value and that's far beyond the scope of what I'm trying to cover here.
Plain margin copies with no other plate markings bring small premiums, generally in the 5-20% range.
If you weren't aware of it, plate number singles have their own catalog. This is a single stamp with a margin attached that shows the plate number. Such copies have a 5-20% premium for common stamps with common plate numbers that catalog $5 or less. Figure a 20-50% premium for items cataloging $5 or more with common plate numbers. Premiums for plate number singles of rare stamps (for example, Scott #245) may be a few multiples of catalog value because so few copies are available. Don't forget to check the Durland Plate Number catalog too. Some plate numbers are more scarce than others and some plate numbers are very rare.
Margin copies of stamps may come with other plate markings such as layout lines, printing company imprints (like "American Bank Note Company"), sideographers initials, and so on. Premiums for these items run in the 5-50% range. The 5% range is more for common stamps like Scott #300. The 50% end of the range is for more rare stamps. Some very rare stamps like Scott #245 may bring a few multiples of catalog value for such a copy. The 5-50% range here is for stamps that have normal plate markings. There are times where a pane of stamps is miscut and plate markings are present that normally would be cut away during the cutting process. These stamps may bring a 50% premium or more depending on how rare this occurs.
Some early US issues were plated by philatelic scholars such as Carroll Chase and Stanley Ashbrook. Some plate positions are more scarce than others. There are a wide range of prices. I can't give you any general price range for plated copies of stamps. You're better off studying that field and learning what the market brings for certain plate positions.
Constant plate varieties exist for many stamp issues before 1920. Printing plates become damaged for a variety of reasons. One of the better known examples of this is the "Broken Hat" variety of Scott #231, the 2¢ Columbian. There is a book written by Loran C. "Cloudy" French on plate varieties on Bureau printed US stamps. The Scott catalog recognizes some of the major plate varieties such as the Broken Hat variety. Premiums for constant plate varieties are small though. Many plate varieties are very tiny and it takes time and a good eye to find them. Most dealers don't look for them because it's too time consuming. Plate varieties recognized by the Scott catalog or those that really stand out like a large crack have some premium. Usually in the 10-50% range depending on the severity of the plate variety and how common it's found.
When you put all of this together, I think you have a recipe for determining stamp values. Let me give you a few real-life examples.
You have a copy of Scott #300. It's a common stamp. The stamp is barely hinged. The catalog value is $50 for a hinged copy. This stamp would sell in the $75 range.
You have a copy of Scott #330. This stamp is notoriously off center. This copy is VF and catalogs $50. Because it's so often found with poor centering, a copy like this is likely to sell for more than catalog value.
You have a copy of Scott #292. It's a scarce stamp with a catalog value of $500. This copy is VF centering, but there is a missing piece of the stamp in the corner (about 10% of the overall size of the stamp). Centering doesn't matter because a large piece is missing. This copy may sell for $25 (about 5% of catalog value). In this case, the major damage trumps the centering in determining value.
You have a copy of Scott #427. A lightly hinged copy catalogs for $50. This copy has no gum and only Fine centering. Because it's no gum, it would have a value of about $25. Because it's only Fine centering too, figure 30% of that $25 figure. Now you're looking at $7.50 for this stamp. It's not uncommon for some stamps to have multiple factors that determine value. In this case, the no gum and Fine centering work against this copy and bring the price down to only 15% of catalog value.
You have a VF, MNH copy of Scott #620 that catalogs $20. You notice a speck of dirt that is on the back of the stamp, but under the gum. This is a tiny natural inclusion on the stamp. Because it's so tiny, the value of this stamp would be in the $15 range.
You have a VF, MNH copy of a stamp that catalogs $10. This copy is a plate number single. A value would be in the $12-$15 range. You open your Durland Plate Number catalog and find that this is a scarce plate number. A normal NH plate block sells for $100, but a NH plate block with this number on it sells for $300. That’s 3 times the value. Apply that same ratio to the plate number single copy. Now this stamp is worth around $45. Suppose you have a second plate number single of this stamp with the same number, but with only Fine centering. Since Fine is about 30% of catalog, this copy with Fine centering is now down to about $15 in value.
I hope this workout hasn't taxed your brain too much. But I wanted to give you some relative figures for the value of stamps. I hope you see now that catalog value is just the tip of the iceberg in determining the stamp value. So many other factors go into it. Catalog value is only a starting point and nothing more.
Ultimately, the market sets the value. The price ranges I've given you are valid for today. Those ranges may not be valid a year or more from now. Things change. The bottom of the market may fall out for Gem and Superb stamps. The supply of a certain stamp may dry up. The market adapts to those changes. Remember that it takes several months to compile and print the Scott catalog. By the time it hits your mailbox, the catalog value may already be a few months out of date compared to the current market. Not that this is a bad thing. It's just impossible to put out something as large and comprehensive as the Scott catalog and have it be absolutely in synch with the current market.