I don't hassle about non payers etc. I will do their windows once and if I do them again with no payment I don't do them after that and that's it.
I don't get stressed or think of revenge except once.
I'd agreed to do the windows of a take away once a week which fitted in with our commercial round perfectly. 4 weeks laters I gave someone in the place an invoice in an envelope addressed to the owner. I called back every time I went past and eventually I caught the owner on his way out the take away. He said to call back the following day at 1pm which I did and he was not there. Apart from the fact that it's hassle to keep calling back especially when I'm working elsewhere, the amount was just £15 (for 2 large windows and a door).
In the end I went down there during the evening and he got all irate with me about how I'd not done this and that and how I'd promise to include this and that which amounted to the whole place inside and out and the flats upstairs every week for £15 a month.
Then he gave me a tenner and told me that a Friday was no good for him and I'd have to do his windows on a Wednesday so as he could inspect the work.
I tore his tenner up into little bits and stuffed it down his shirt much to the stunned amazement of the customers waiting for their take aways. How I didn't thump this moron was a miracle. I took a deep breath and walked away.
The following day, and I would never normally dream of doing such things, I sprayed a large can of WD40 over all the wndows.
You should now see his windows 8 weeks on.
I also do the shop next door and every week I knock on the window and wave to them with a big smile.