Not me but a family member, free-lance programmer / IT consultant.
His first big contract after starting his business was often a little late paying him. It's normal in that type of business, they have 90 days to pay and sometimes the person hiring you is waiting for money from investors, clients, etc.
After working for him for months, he shafted him on the last 2 months of work. Disappeared completely, ended up losing 10,000$ in unpaid wages. This is shortly after my family member was forced to work on Christmas and never had a chance to really take his holiday off because the guy called him in a panic for all kinds of things (non-urgent things) every freaking hour.
He never took it to small court because he was completely broke at that point and couldn't afford anything. Would've taken years and he probably would've just lost more money. Surprisngly, he kept going with his business and it's gotten successful now after that pretty big scare.
He definitely learned from that mistake though, doesn't send final versions of anything his clients could disappear with until he's paid and keeps track of everything more tightly now. He had another scare last year with some big clients being late (and it's a huge contract that even has him employing a few other programmers at premium rates) but eventually he got all his money, though months late. He usually works on a few smaller contracts as well to keep his business running especially if he loses a big contract and it's definitely scary when they are all late on paying at the same time.
Justice porn : A few months after he got screwed over, a friend of the guy who screwed him over wanted to hire him for a job. He negotiated to be paid upfront, ending up doing half the work, dropped it, and told the customer to ask his friend for the rest of his money back because he owed him 10 grand. Not too sure how legal that was (well, I am pretty sure it's just as illegal as the first situation) but none of those involved ever contacted him again after that or pressed charges. Wish I could've heard the conversation between those two though.