the chances of getting a defective part are slim to none.
i have bought whole lists of parts for customer builds from ncix multiple times, as well as my own parts for my rig. never had a defective part except for a 7900GTX that had a dent in one of the heat pipes (which isn't really a defect, its called physical damage). I called them up, and they paid for purolator air both ways. I do spend a lot of money there, so I guess they treat me nice, but honestly I would bet an arm and a leg on the quality of service NCIX provides.
you wont be sorry you bought from them.