If you're on the Internet looking for stamps, you should check out the Stamp Collectors Against Dodgy Sellers (SCADS) website at www.scads.org. It's an informative website that exposes some of the fakes and alterations floating around on the Internet including eBay. I invite you to check out this useful website.
I buy and sell some material on eBay. I do browse eBay for items that I may be able to use for my business. I see a lot of good items on eBay. I do see a number of items that are altered, mis-described, of downright fakes.
There is no free lunch. For example, if you believe that you can obtain a VF, MNH copy of Scott #1 on eBay for $500, you may be in for a surprise. Such copies are very rare. The chances that the average person down the street has a copy for sale on eBay are incalcuably small. You have a better chance of being hit by lightning. Chances are, the item you're buying is regummed at best. Or more likely, it's a fake.
On a related note, I've seen recent items listed on eBay for sheets (or part sheets) that are reproductions of scarce US stamps like the dollar value Columbians. In the wrong hands, I'm afraid that these items will soon show up on eBay as fakes madquerading as the real thing.