Be on the lookout for any low-quality knockoff or imitation leather. Only a genuine leather jacket has the toughness needed to keep you in one piece. A biker wearing fake leather might as well be riding shirtless.
The product description should tell you everything you need to know. If a jacket is listed as full-grain leather, top-grain leather, cowhide, or sheep leather then it's the real deal. Anything listed as faux leather or genuine leather, which is in fact not genuine, is a sign to run for the hills.