Bro i am assuming that the work on your car is being done in your absence. true?
If i go to mechanic even for brake service i do get my hands dirty with them like i be like assistant to make sure everything is doing ok. Because acha sa acha mechanic b dandi mar deta hai ya koi ek bolt nut skip kar deta k dekhe is ko kuch nahi hota apni jaga mazboot hai etc etc.