Stamp collecting is a popular hobby. Though stamps are usually more valuable when they are not used, old and rare stamps that are used still retain value as a result of the rarity of the stamp. Collectors will still buy a used stamp for a collection, if the stamp is hard to find. Even common and new stamps are sold to collectors after being used, though they do not sell for high prices like rare and uncommon stamps do.
Remove the stamp from the paper so that it is not damaged. If damaged, the stamp loses value. If removing is too difficult, tear the envelope around the stamp leaving plenty of room so that the stamp is undamaged. Then cut the paper down until it is near the edge of the stamp, but does not cut into the stamp. Leave a little extra paper around the edges to ensure there is no damage. Sell it on the paper so that the collector can remove the stamp. Damaged stamps have very little value.
Organise the stamp or stamps. If selling several used stamps, organise them so that similar stamps are placed together. Selling individual stamps is usually less valuable than selling themed stamps as a small collection. For example, a buyer would pay more money for a set of six bird stamps from the same year than they would pay for the individual stamps.
Look the stamps up in the Scott Postage Stamp Catalog. The Scott Postage Stamp Catalog shows stamps from around the world and gives a basic value for stamps. Used stamps are usually not valuable, unless they are very rare, but identifying the potential value is important to the selling process. If there are rare or expensive stamps, the catalogue will show them. This gives a good price point to sell the stamps in.
Take the stamps to an American Philatelic Society dealer. The dealers that have joined the American Philatelic Society will often buy stamps to sell them to collectors and act as a middleman. Keep in mind, they will buy at a lower price than they will sell so that they can make a profit. Sell the stamps to the dealer if the price seems appropriate. If not, there are other places to sell.
Post the stamps on an auction site. One of the best ways to sell a stamp collection is through eBay or a similar auctioning and selling web site. Collectors will find the used stamps and make a bid or purchase according to the purchase price listed if they want the stamps.
Locate a local stamp club and take the stamps to the club. Collectors gather at a stamp club and might want to buy the stamps for their personal collections. This is a direct sell to a collector, so the profits might be higher than selling through a dealer. Keep in mind some stamp clubs might accept donations, such as a school's stamp club for children, and might not wish to buy or the members of the stamp club might not want the stamps if they are newer stamps or common stamps.