Replying to Gamestop trade in help

hey guys im trying to figure out how the gamestop trade in works. my nearest gamestop is about 15 miles away so i dont want to make a trip for nothing. I have like 11 games that i do not care to have anymore such as: black ops, mw2, cod4, test drive unlimited 2, mx vs atv reflex, and a few others. I just want to know if there is like a limit to how many trade ins. What percentage i can get. I just want to save some money and buy either mw3 or bf3.....help