To find out what old postage stamps are worth, do a little research into the specific stamps, and be careful in identifying the stamps correctly. Some stamps have common and rare varieties which differ from one another only in minute details. Usually, assessing the value of stamps is helpful in weeding out what is not valuable, while valuable stamps require additional appraisal by experts.
Check the condition of the stamps
Mint stamps that still have glue on the back are worth more than used stamps. Sort out stamps that have creases or tears, which are worth less than those in excellent condition.
Compare prices online
Check online auction sites, such as eBay, to see what prices are being asked for the stamps you are interested in. Make sure you are comparing your stamps to stamps in the same condition, as a stamp in poor condition can be worth around 10 percent of the value of the same stamp in perfect condition. Reduce asking prices on eBay by 20 percent to account for the fees charged on the site.
Check stamp price guides
The key price guide for stamps in the United States is the Scott Postage Stamp Catalog. Check your public library to find a copy, but check the publication date of the catalog before using it. Catalogs that are out of date provide inaccurate prices since stamp values in the United States have decreased since the 1980s.