Not the original person you asked but I do the same thing and I would buy them a new one if I damage it. I'm confident that I'm not going to damage their things.

And if it's something where I'm not confident, or its not replaceable / way too expensive, that's when I'll decline. But typical computer repair or building is really easy and safe. Need help delidding your CPU or some other uncommon thing? I'll give advice but I'm not handling it.