Are used stamps worth less? How is the value of a stamp determined?

 

Used stamps are not necessarily worth less than an unused stamp but generally are. 

Take the most expensive stamp in the world for example, the One Cent Magenta from British Guiana. This is a used stamp of which there is only 1 in existance. In 2014 this stamp was sold for approximately £9.5 million pounds.

In philately, a mint stamp is one which is in its original state of issue, is unused, has never been mounted and has full gum, if issued with gum. The term applies equally to postage stamps and revenue stamps. 

In practice, the term is used within philately to refer to any stamp that appears to be unused, including those without gum, or previously hinged.