There are some clues that you can look for. It might be in the form of a circle, a box, or a maple leaf. It's called a blind stamp, and occurs on the lower corner of the back cover nearest the spine, and is impressed into the cloth binding under the dust jacket. You should beware of books which have no price information on the inside front flap of the dust jacket. This is not a rule however, as many Canadian titles never had a price on the jacket, as well as books produced by some University and small presses.
Some book clubs use a statement on the inside front flap of the dust jacket.
Some publishers have primarily published reprint editions. But there have been many others. In order to be sure, check the copyright page and see whether it matches the publisher. J.M. Dent , then you've likely got a reprint. As for reprints by the same publisher, that can get a bit trickier.