It depends...
Are they scratched/dirty?
Are they in their boxes with their instruction manuals?
How old are they?
Like for example, I traded in approximately 30 games. They were all a little dirty, most of them didn't have a cover, and most of them weren't very new, and were very old. I received $45.50 store credit. While, at the same time, my cousin who traded in approximately 7 games that were in great condition, kind of new, and had their cases and manuals, received around $60.00 store credit.
I might not have helped, but you can call GameStop/EB Games and check. Visit http//gamestop.com, then go to Store Locator. Enter your zip code, and, well, I guess you know what to do next.