A lot more employees just don't seem to have any common sense anymore...
I've taken back plenty of games with GS stickers on them, even games from blockbuster. The only requirements for trade-ins were that they had to have the cover art, instructions, and the disc could not be cracked. Someone could have scratched their name in the disc and I would still take it.
Systems are another story. As long as they had the cables and one controller, you could trade it in. That was the only requirement. We did not have to test the system to see if it worked. I've had so many DS systems traded in I knew for a fact didn't work, but hey, I'm following the rules.