Is there a place to find GameStop's values for retro games? And is it modern retro like PS2 and GameCube or old school retro like the NES and Genesis?
Call them, and it's mostly any popular older game (anything that sells for more than $15 is fair game, even OG Xbox). They even take accessories, but not memory cards.
There's no directory, an employee should be able to help you though if it's not a million games.