I had to do something for my business class, and what I did was I went and bought a brand new game from Gamestop $59.99. It was the last one in stock (I purposly pried to get a game that was last in stock, the game was GTA IV) I stayed in the store for exactly 5 minutes looking around, and then went to the counter and said "I wanna sell this" so he was like 'srs' I said 'yes' he gave me $13 for it. When it was still in its foil. When I walked out of the store, I saw him put it back on the new release shelf.
Since then I haven't gone to Gamestop for ANYTHING. if I need to sell a game, I go to a store around here called Disc Replay. They give you 3$ off of whatever they sell it at. If they sell it for 50 they give you 47. I know for a fact they do that for everything because one of my close friends works there.