I agree 100%! GameStop and other game stores, should adopt a condition based scale for buying and selling used games.
Could you imagine buying an Amazing Spider-Man #1 comic book used in any condition you wanted at a set price? What condition would you buy it in? Near Mint/MINT, right?
Why don't we, as video game collectors (and gamers) demand that video game stores treat games as collectibles? When someone brings in a game for trade and gets less for it than someone else who has a "near mint" copy, maybe people would learn to take better care of their items and every collector would benefit!
There would be some "kinks" to work out (grading scale, etc.), but its ashame that we have to settle for less!