+1 for tipping!
In fact if it was lunch time, I would wave off the tip and ask if they’re hungry. If so, I would ask if they’re willing to take a trip to the small sandwich shop across the street, by the time they come back, I’ll have their bike all set and they would hook me up with a sandwich or snack of some sort.
I find people are more willing to tip in food over cash.
As for pay….you cant play the "averaging" game. Shop size and clientele is too wide spread to make generalizations. If your a mechanic and you want a good pay, you better find the best shop you can that sells high end bikes.