count it as a loss this time, but I would phone the customer, politely explain that if you are not going to call to clean his windows, or if you plan to send someone else you will always notify him in advance, hoping that will clear up any confusion in future, expressing your high regard for both customer and w/c loyalty.
If he doesn't accept...you loose. If he accepts, you gain back £23 and slam the door on underhanded methods.
What have you got to loose.
Yesterday I did a house near me, I was a bit late, (I'm always late at the nearest ones), the lady said she was going to ring me, she recieved a note through the door from a windowcleaner stating that he was taking over a number of clients in the area and expanding in this area. A very ambiguously worded flyer. She thought he was taking over for me. How kind!

I explained that if I am ever in that kind of situation I will notify my customers first.
She thanked me, and said she wouldn't trust someone who used that kind of crafty way!
I'm afraid it will only get worse. Keep it up mate, it beats working for a living
