I advertise, that I offer a regular, reliable, quality window cleaning service, and I do my best to adhere to that.
But, in return, I expect the same from my customers; it works both ways, in my book.
It's taken years, but all my customers are good (yes they cancel for building works etc but none take the p1ss).
When a customer comes along that is 'NO GOOD FOR MY BUSINESS' they get dumped (very politely, but they still get dumped).
Some people would argue that they 'need the work' so will put up with it.
I would say, DUMP, and spend the time getting more customers.
You can never guarantee the type of customer you're going to get, but you can decide how you move forward with it.
Always, always be polite.