I figgure that if it wasn't run over by a truck, and it looks OK and the price is right, you can't go wrong. Even if you have a problem, it can be repaired. They're relatively simple to work on, just look for one that is in good shape, whether a G2 or any "old style" Contender.
Some folks say that the really old ones have the best trigger, the Easy Open is the cat's meow, and others say the G2 is the way to go. Some folks like me have a nice collection them all!