mspecperformance

It seems like you are in a position of "jack of all trades, master of none." You have 3 businesses going there from auto body, auto repair and car sales. There are a lot of guys who have done all successfully but everyone's path is different. To see the best results you definitely have to pick 1 and run with it. If auto repair is where you think the best opportunity is then awesome! If your issue is not having a qualified tech I would suggest to hit the ground hard on recruiting. Leverage any opportunity you have to look for a great tech. Once you have some candidates my suggest is to vet them thoroughly. Worse thing is to get into bed with a bad employee, trust me I know and most of the guys on here can attest to the pain you'll go through.

2 possible scenarios I see...
 
1. It is possible you did not properly communicate everything you just laid out. Did you personally speak to the customer? Did a service advisor speak to the customer? Maybe something got lost in translation when you were explaining you did not want to service the front brakes due to them being very new.
 
2. The guy is a total douche bag.
 
 
Do you perform digital inspections? If you had visual proof that his rear brakes were in need of service then you could have rebuttal stating facts and proof instead of your word against his.
 
 
Man I feel for ya. I am really tired of these whiny baby customers as well. Besides that we are having a record slow week so far so I am pulling my hair out.