I get stuck with a lot of Solid State junk for repairs.... The same basic diagnosis methods work with tube gear, but It takes me ages to completely troubleshoot solid state. So if I charged for real hours it wouldn't be worth it for most people. If they are truly in love with a piece of gear, then I tell them I'll do it.
Yes, the troubleshooting is what would worry me too.
I do the same with building tube amps;taking too much time and effort.
If I charged the "going rate"......oh Lordy.