There are a limited number of professional stamp expertizing services that operate in the US: the Philatelic Foundation (PF), Professional Stamp Experts (PSE), American Philatelic Society Expertizing Service (APEX), and Professional Stamp Authentication and Grading (PSAG). Also, the Confederate Stamp Alliance expertizes Confederate stamps. There may be others, but those are the ones Iím aware of and I know they are reputable organizations.
There are a few individuals who expertise stamps such as Bill Weiss. Bill has expertized stamps for other agencies for many years and he now expertizes stamps on his own too. People like Bill have many years of experience with stamps and they are quite knowledgeable.
Recently, Iíve seen instances of stamps being offered with certificates from people or places whose name I donít recognize. Thanks to todayís inexpensive computers and laser printers, itís possible to print some really professional looking certificates.
Iím sure some collectors fall for these schemes and waste their money having their stamps expertized. However, these certificates are meaningless to me. Unless the certificate is from one of the major services or a highly respected individual, the certificate is garbage. To me, it looks like more people are trying to jump on the band wagon and issue their own certificates. Maybe this will subside now that the market for graded stamps is settling down.
If you see certificates from places youíre not familiar with, run the opposite direction. Only deal with certificates from recognized sources. Youíll be glad that you did and you wonít waste your money.