Your customers are paying the prices that YOU set and have set yourself over the last 11years.
Giving tips isnt a given requirement nor a legal expectation at december for window cleaners or the like. So if this isnt a wind up, your bang out of order for doing so.
Wonder if this story makes the paper.
Do you honestly expect people to be really grateful to you for being emoloyed by them in the first place! How would you like it, if after ordering your food at zay mcdonalds, whilst on lunch break and they had X amount extra as a tip. Or same principle at a restaurant??
Do you leave a tip when you go for a meal, or the hairdresser, the postman or even binman.

If your giving yourself a tip, then im guessing you dont

Heres a tip.........if you want more money, do it legit and get some more work or put your prices up accordingly.
Another tip, ask your clients if they want there windows cleaning this month because there is an extra 3quid applied in december and not the usual fare we agreed upon!!!