I had a case recently with an ex-customer who owes me a fair chunk, but I cannot, and probably will never, get my money from her. She treats workers like her personal slave, and I sacked her off when I had had enough (not soon enough as I really try to see the good in people but she had gone too far with her mickey taking).
She saw me cleaning a few doors up, and called out to me to come over. I waved and called back 'OK'. When I finished the house I was doing, I loaded up and drove off.
Felt great!
I am back there this week. Looking forward to it.
John
Like that!! 
UPDATE:
I was in her road again yesterday, and, yes you've guessed it, she called me over again!
I waved as before, and called out 'OK!'. To make sure I was going to call this time, she got in her car and drove over, repeating that she wants me to call.
I reminded her that she still owes me 60 euro for previous cleans. She said she will pay me, to which I tell her that I will do them when the money is in my hand. She agrees.
When I get to her house, she points out that one of her spot light bulbs in her fascia boards needs changing, so can I change it for her. I say 'yes, when I have been paid'. She says 'It's only a bulb', to which I reply 'and it's my time'.
'But you will be doing the windows as well!' says she. 'When I have been paid', says I, adding 'I'm sorry if I sound harsh, but I've been screwed over too many times, and I cannot afford to work for nothing.'
The upshot of this is that I still didn't get my money (I didn't expect to) but she still has a duff fascia spot light, dirty windows and no mug to clean them.
I feel even better than I did last time.

John