While there are no "sure fire" ways to tell if these types of books are legit, there are things you can look for that will give you a pretty good idea. Photocopying was prone to fades back then, and individual machines would develop particular patterns. The machine Kevin and Peter used tended to have a fade stripe toward the right hand side of the book. The result of photocopying a photocopy would make that fade vanish.
People who have handled a large number of these books (Myself, Danny, Rich, etc) can usually tell fairly easily when they are in hand.