Gamer systems can be a pain, but a nice upsell too. Case in point, we usually make 250-500 on a gamer rig because we buy the parts and install them. I helped a guy recently and made good money, he'd built his own gaming system, and it was overheating and shutting down. I ended up selling a new board, new case, and installing it all. He came back a couple of months ago with another issue, actually it was doing the same thing again. It was overheating a little, but the board was feeding the cpu stock voltage, the cpu was having none of it. He was using a raidmax power supply that was supposed to be good, personally I don't use raidmax products. I like my EVGA and Corsair PSU's just fine. But anyway, installed a small closed loop water cooler on it, and had to turn on load line calibration in the bios for it to stay stable. So far knock wood, he's not been back.
You'd be surprised how many kids watch a little youtube and think they can build a gaming rig. I have seen people bring them in missing the io sheilds on the back, sad really. Some of them have top notch components but if they only would take the time to set them up right. I had one guy in probably his 50's bring in a system with a real nice Asus board, high end stuff. Top PCI slot in the board was going out. He wanted to know if he could use the other slot. I finally convinced him that board would likely have more issues that he needed to RMA it. Ended up selling him a Gigabyte board, haven't heard of any issues in a year or so since then. Gaming systems can be a pain, but can make you a little cash here and there if you are patient and know what you're doing.