A client I did some work a while ago for didn't so much refuse to pay but just didn't pay. Excuses, ignoring emails/calls etc. After about 7 months of this going on, I told them that they had 5 days to pay otherwise the only copy of the site I'd built for them was going to be deleted and I'd just accept the loss.

The website wasn't actually live at this point but obviously they wanted it live because they paid up fairly promptly.