I watched him roughly rip out the insides of my desktop, as "the plastic had melted and it was really hard". He told me he'd been around computers all his life, so I left it, because surely he knew what he was doing.
Big mistake. I get so anxious when other people touch my technology because it always seems to go wrong, and this was no different.
On this class of machine, it's not particularly easy to swap a whole motherboard, and there are many steps that must be performed.
To a person not trained in computer hardware repair, I'm sure it looked like that. However, I can assure you that all he wanted to do was to install that motherboard and fix your computer.