Personally I have had a few times when customers have pulled a fast one, siad the work was not good despite no complaints and waited 3 weeks to tell us!!! I just take a step back, handle the problem as diplomatically as I can and retain a professional stance.
However, I did have one new customer call me in tears to say that her previous window cleaner who had not been back for 6 months suddenly appeared. She told him she had made other arramgements to which he was very p***ed off about. He then went away, returned later with lots of mud and proceeded to smear all of her upstairs and downstair windows with it.
She called the police and as he had caused NO actual damage the police wouldn't follow up her complaint.
Its a crazy world out there!!!!!!!!!