I think you need to be a bit more pro about your bussiness if that was first time they said leave it then y tell them to stick it but if its happened on a few ocasions then fair enough . 
I only work for people that can keep their end of a bargain ... call me old fashioned like that .. used to give them 2nd and even 3rd chances but once a messer ALWAYS a messer.
World is full of proper customers however world is not full of proper window cleaners so I can easily replace them which I have already.
The terminology or ethos of being pro applied to my business means me putting me and my family first and NOT messers as they will damage my daily earnings potential and to allow that is both unproffesional and naive.