Papajin,
I've been trading on LaLa since last June and have found the service company itself to be very good and quick to responded to Q's and a problem or two, for instance recieving the wrong CD. Since you're actually dealing with individual traders, the cd condition is dependent on the sender and even there I've only had one cd which had a skip. Once you report a skip or non functioning cd it is removed from your trade records and you get your 'credit' back. The clam shell cases provided for mailings are usually okay, but on occasion they can 'buff' a spot on the cd surface with bad usps handling. This is easily prevented by laying in a sheet of lens cleaning tissue etc and there are blogs on site with other shipping tips as well. pm me for more info if interested.
I really like Amazon's used cd dealers too, good prices and the cd condition always seems to be as stated. Far more reliable than GEMM from my experience.