Loss, my ass. When you bring in your copies of Madden 2002-2005 and get 50 cents to a dollar in store credit out of it, it just gets you to go spend 50 bucks on the new one. The game trade-in has nothing to do with selling used games but with selling new ones.
By the way, here's a GameStop shopping tip:
When you're buying a used game,
ALWAYS ask to 1) see the disc and 2) ask if they have a better copy. They always try to move the shitty, scratched up copies first. This has happened to me at every GameStop I've ever been in, including GameStops in 2 different states, so this isn't just some quirk of the store I happened to be in.
For example, a few weeks ago I bought a used copy of Final Fantasy XII, and they hand me what appeared to be a former rental copy with some nasty scratches on the back and some permanent marker writing on the front (which PISSES ME OFF

) so I asked to see another copy and they sigh at me and pull out a nearly flawless disc. Assholes.
Speaking of which, they just released FFXII in greatest hits, so if you've been waiting to get it, now would be the time.