There are definitely better places to post this but I'm gonna throw it out here anyway…
I'll tell the short story then add some TL;DR afterwards.
Built a PC for a friend - everything new except for the GPU which is a used 1060 I got off eBay. He takes it home and starts experiencing frame skipping and game crashes while playing WoW and Skyrim. He tries to fix it, makes it worse, gives it back to me. I fix what he's broken, set up the PC again and run Heaven for roughly 6 hours at Ultra settings without any hiccups. Give the PC back to him, he takes it home, then says that he's experiencing the same issues again.
This doesn't make sense to me - how could Heaven run fine but he's experiencing what seems to be performance issues when running some low end games?
Now for the potentially relevant TL;DR story of his own troubleshooting attempts. So when he tried to fix it he's opened up the PC, thought the RAM was in the wrong slots, taken off the CPU cooler to get to the RAM, put the RAM in the 'right slots' (the wrong slots), then just slapped the cooler back on without cleaning/reapplying thermal paste. He didn't tell me any of this and I only found out after running a stress test for about half hour and hearing the CPU cooler fall off. The motherboard backplate had fallen off when he'd tried to fix it so he hadn't actually screwed the CPU cooler into anything. His GPU doesnt have a backplate so the CPU cooler fell directly onto the GPUs PCB. I've since taken out the motherboard, retrieved the backplate, put the RAM back in the right slots, cleaned the CPU/Cooler with iso and reinstalled with new thermal paste.
Specs:
Asus nVidia GeForce GTX 1060 Dual OC 6GB GDDR5
AMD Ryzen 5 2600
Gigabyte B450M DS3H mATX
Kingston HyperX Fury 16GB (2x8GB) 2666MHz DDR4
Corsair CXM Series Modular CX550M
Holy crap. He's lucky the only consequence was that the computer crashed in some games and he didn't basically short out and fry the whole system.
I'm sorry but I think you have an idiot for a friend. I hope you've also now padlocked the case and slapped a warning sticker on it saying "Don't f***ing open this again".