You will find most people are happy to pay for quality work. You run a quality workshop, you provide quality work, 5 out of 10 customers will still get their alternator overhauled and fit a new battery even if its just a belt problem. 5 out of 10 people are more than happy to know, everything is good as new now and this will have reduced there down time from work due to future problems being just that - something not to worry about for the distant future.
Its called Quality service, Not Dodgy service.

Service - To maintain