That just sounds like you're being taken for a ride
If I'm helping then I refuse any kind of money. I don't give guarantees or service like a business does, I don't want money like a business does. I do often ask that they try to learn from the experience, I'll gladly explain everything I'm doing.
The other option is I refuse, for whatever reason that is.
This keeps my choices those of a friend and my responsibilities those of a friend. I like keeping them that way.
Anyone else I am happy to sit right next to them, happy chat and advise, be a pair of extra hands as required.
But I won't sit there while they walk away and do anything else.
If it isn't worth THEIR time to fix it, it isn't worth mine.
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.