According to Stamps.org, valuation of a stamp collection depends on many factors including the age, rarity, condition and demand for particular stamps in the collection. The easiest way to get a fair valuation is to have a collection evaluated by an expert stamp collector or dealer. When seeking an evaluation, one must tell the assessor which type of valuation to give: tax value, sale value, insurance value or donation value.
The American Philatelic Society explains that a formal appraisal need not be conducted unless required for legal purposes because appraisal fees can be steep ? perhaps $50 to $100 an hour. One can find a reputable expert to conduct either an evaluation or an appraisal through the American Philatelic Society or the American Stamp Dealers Association.
A non-expert cannot value a collection, simply because the differences between a stamp valued at hundreds of dollars varies only slightly, perhaps only by a crease invisible to the naked eye, from a stamp worth $10. With American stamps, condition is everything, including the perfect centering of the printed image and flawless-perforations around the edge.
Generally speaking, early, unused U.S. stamps with the original gum on the back can be valuable, in particular stamps made prior to the American collecting boom of the 1930s. In the 1930s, the U.S. Postal Service increased the amount and variety of its stamp production in direct response to the collecting wave.