As with coins, baseball cards, comic books, and even rock posters, in recent years some stamp collectors have started submitting their stamps to grading agencies for "expertising." A few of the best-known organizations that issue certs for stamps include Professional Stamp Experts, the Philatelic Foundation, and the American Philatelic Society.
Some sellers list their stamps for sale with an existing cert, while others will offer prospective buyers the opportunity to have a stamp graded and examined by a third party before completing a transaction. If the two parties take that route, though, they need to be patient. For example, the American Philatelic Society warns that its average American Philatelic Expertizing Service, or APEX, certificate takes 45 days, and parties should plan on 90 days, with fees tied to the value of the stamp, as listed in the Scott Catalogue. The good news, though, is that an APEX cert guarantees a stamp to be authentic for values up to $5,000.