My anti-doormat policy is to walk away and not go back.
It may seem unprofessional, but I have to be seriously miffed to do it, and I would always walk away rather than lose my cool. Have met some of these ex-custards when I have continued to do their neighbours windows, but never, ever has one of them asked me to my face why.
The main cause of me walking away are persistent messing about over paying. I get on with most people, so personality clashes don't figure at all here.
John