I have a real distaste for cold callers (sorry Mr Bizz). I don't care if they are trying to sell me newspapers, windows, politics or religion my default response is to tell them to go away.
A window cleaner though, I may not be so angered by the rude interruption to my time off. Although I'd be very surprised that he missed the landys all stikered up on the driveway.
Get a price. Then, ask to see his window cleaning license....