In my experience with FYE, everything is a complete YMMV and differs according to every store, and even employee. I've done this three times with about 6 games each time.
The first at store 1 I was given $10 credit for each game, but not the sports games, toward whatever used games I wanted.
The second at store 2, I was given $10 for each game including my ESPN 2k5 games, towards whatever used games I wanted.
The third, back at store 1, I was paid $1 for each game I traded in and the $20 games were zeroed out and given to me. I didn't even get a receipt for that one.
Such a strange and horrifically led company.
FYI for everyone, they also have some iPod rebates going on right now ($50 for 80 GB, $30 for 8 GB nano). I know that their rebates aren't the most reliable, but I've had good success with them in the past, and when its cash back for my credit, its worth it. Thats what I'm doing this flipping for.