I repair stuff occasionally for other people, either because it's something interesting, or because it's for a friend.
Three rules:
Nothing gets left at my place. I'm short enough of space.
The owner is present whenever I'm doing anything (They can put in as much time as I do) No show, no do.
I'm not interested in anything the local TV shop can handle. They have a living to make and they're a lot more efficient at their sort of stuff.
Without these, I'd get exploited. As I'm not doing it for money, I get to be dictatorial.
You could have had a little fun, Phil by saying you'd use a different make of tester. Someone wanting to use the valves would be fine, but someone wanting to auction them would see their value dropping
David