There are a few factors that govern how valuable a stamp is to stamp collectors: the most important
is how rare it is. Obviously, very old stamps are uncommon so these, such as the ‘Penney Black’ very
seldom come up for sale and so are unbelievably expensive. Other things that might make a stamp rare
might be where a mistake was made in the printing and the stamp was withdrawn after only a few had
been sold. Undamaged stamps are more valuable than similar ones that have been damaged.