I once did a series of illustrations for a publisher who produced a quarterly children's annual. He didn't pay me and wouldn't answer my calls. I came up with a plan. The next time he needed a small piece of art, I agreed to do it, but rather than mail it to him, he had to come to my home and pick it up. When he arrived, I refused to give him the art until he paid his bill. He said he was broke and would do anything to even things up. I asked him to mow my lawns, which he did. I still savour that image!