Would gamestop take back my game?

So let me get this straight.
your buying a game and then going to sell it back?
Thats a bad idea.
Instead:
1.)buy it used from game-stop
2.) then sell it on amazon.
Game stop buys games for way way way way to low.
If you sell it on Amazon you will make at least 40% more profit.
If you plan on doing this more often I would recommend getting game fly. ( a NetFlix for games)

Already buying it used obviously, and I'm not selling it back, it'd be a return.
I know they take back USED games within 7 days of purchase, but would the same apply for a used Rock Band ?
Basically, can I return it a day later, they'll take it back, and I get a full refund?