I had a Winter canceller a few weeks back. I had only done two cleans for them as well. This hasn't happened for years now. I made it clear to him that I would probably have more work by then and if that was the case, I would not be able to start cleaning his windows again (I wasn't entirely honest there because I have not got the slightest intention of working for him again). If I was uncertain beforehand, the bit that made sure I wouldn't do his windows again was when he said "You'll do them". I broke my own rule there and made a decision based on emotion rather than business sense because I decided there and then that even if I was short of work, I would not re-start for him in the Spring.