I've been lucky then.
The only work I've had to put into any of my machines is a "clean and oil". I don't like to "mechanic" on them...just not my thing. If they need more than a clean up, they don't come home with me.
That opinion would change, of course, based on rarity of the machine. I'd tackle more complex repairs if the machine was a rare one...but we all know how rare rare machines are!!