CAG needs to quit advertising Gamefly as selling "Usually excellent condition games"
I guess it depends on your luck, but I'm in the same boat as you. Very hit and miss, to the point where I'll look at this thread for the prices, but won't ever buy from them. I've bought games for myself to play that outright don't work. And I've bought games to trade in (PS3 blu ray discs, to boot) that are chipped and even Amazon won't accept them for trade-in. I hate Gamestop, but their discs at least work for me.
What makes it even easier for me to pass up these "deals" is that I'm obsessed with Skyrim and there's not much time for any other games for the next few months.