I have purchased 100-150 PS2 and Xbox games from Gamestop over the last 2 years. I also, have picked up 10-20 360 and PS3 games. All have been used.
I have alot of stores in my area and the guys at the stores generally don't like me. I inspect each disc and if its not to my liking, I ask for a new one. I get their response by saying that all games are guarenteed for X number of days but the reality is that I'm probably not going to play the game in the next few months anyway. I come back by saying that I'd rather spend an extra 5 seconds to inspect the disc at the store rather than going home and realizing the game does work. Again, the employees generally don't like my response.
I purchased the Edge card towards to begging of my purchasing binge. However, I do want to complain that there is one store in particular that I will not go to. I bought one $10 game and I wanted to leave. The guy kept pushing the edge card on me and even after I insisted that I didn't want it, he replied by saying "What, you don't like to save money?". I replied back and said that it wasn't worth it to save $1.00 and took down his name and called coporate. I felt cheap! Coporate did call me back (GM from an area nearby) and agreed with me. I didn't ask for anything.