Did you ask for the discount or did they offer it?

Staring at a tower and already mentally ordering a power supply is basically a personality test for techs, and we all fail it. That pinched SATA cable is the perfect example of why the boring answer is usually the right one, because a wire rubbed to bare metal against a drive cage is about as obvious as it gets once you actually look. The urge comes from experience too, since nine times out of ten it really is the PSU or the RAM, so the brain just skips straight to the ending it already knows. Problem is that tenth time humbles you in front of a customer and you eat the cost of a part you never needed. What works for me is forcing a first pass with no tools at all, just eyes and a flashlight, before anything comes out of the case. It slows you down enough to catch the dumb stuff first.