I had a customer who refused to pay the final amount (my profit) because his wife didn't like the sink being a rh drainer, she wanted it lh. The customer had agreed all the kitchen layout with me at the start and I had checked as I went along, the wife only appeared from spain after I finished the job..
I sent my wife round first (she is a terrier) and she got some money and after he sent me a letter again refusing payment, I went along, nice as pie asked to look at the kitchen and its problems, took some photos for the record and got my tool bag out of the van.
Asked the customer to turn off the mains water (as it was buried behind all his collection of rubbish) so I could move the sink. When he had, I removed anything I had supplied ie: service valves, S bend on the waste, cut back some of my 15mm copper and capped off the hot and cold to the sink. Packed my bags and went to leave now that the customer had seen what I was doing and demanded I go.
Then he saw the problem! asked me to put it right and offered a cheque, which I refused and lo and behold £600 cash appeared there and then, I gave him a signed receipt and left.
He was not happy, but I explained the work now involved was an extra as I had done the job once, handed over all the parts removed in a tesco bag and left. Never heard from him again.
Note: if you go down this route, be polite and reasonable and not threatening, you have to be invited in and once the customer asks you to leave, do so immediately without fail. Do not cause any damage ie flooding and only remove what is legally yours. On estimates and quotes alway state that goods supplied remain you property until paid for in full.
Have fun and be careful