To be honest I don't even buy used games. Why? Because gamestop will sell you a used game for 5$ less than a brand new one and it will have chicken grease and scratches on it and you will be lucky if the manual is in good condition or there at all.
I'm picky about the condition of my games, especially since dirty or damaged discs can damage the system's laser.
I know the market is big for used games since people are looking anywhere they can to save money, but if I can afford it I'll always buy new anyway.
Oh, and I'm still against online code or other fees from a used game. Mainly because I like the idea of physically going to a friend's house and playing one of my co-op games with them in person. It beats this age of "online-only if you want multiplayer" gaming market these days. Long gone are the days where people actually got together to enjoy games together, and that feeling gets lost over the internet.