My girlfriend just took advantege of this deal. We walked outside and she turned it on. Both of us realized that the clerk had forgotten to give us the wall charger.
She was hoping for a pink DS, but it didn't occur to her that little girls also own (or in this case, once owned) pink DSs. The first one was covered in these huge, half pealed off Strawberry Shortcake stickers and the second one's top screen hinges were broken and wouldn't stay up or lock into place (Makes me question the quality control of Game Stop even further... and if the person who traded it got the same amount as the person who traded in a good DS).
So, my only advice is to check them out yourself. Make sure the screens aren't all scratched up, check for dead pixels or any weird screen problems, make sure it has a stylus, and finally that you get your wall charger (preferably the official Nintendo one).
Heh, I'm almost tempted to trade in my old blue DS... but I can't justify trading it in for basically the same thing.