I wanted to sell an extra copy of a brand new unsealed game to Gamestop and they refused me. They don't take games like that unless it's a return. Thankfully, my friend had a friend who really wanted the game so I got $40 for it instead of the $25 Game stop was offering me for a opened game. I had offered to open it in the store and they still said no. First time I ever heard of that happening.
Best bet, ask your friends if they have friends who would want the games for a better deal.