I was reminded by my good friend Bronwyn that there are times you have to tell the customer to go fuck themselves, in fact you have no choice but to tell them to go fuck themselves, and I have been known to do just this. There are limits, and no matter how good you are, there are people who are going to step over the line and you can either tell them to piss off, or get trampled on by them.
The story that comes to mind happened when I was still sending orders directly to people's homes with an invoice so they could send me a check after delivery. In this particular instance, I sent a vase, I waited about 10 days, no check. I called the customer's home to give them a "friendly" reminder. The customer called me back and left a breezy message on my voicemail. "Oh," the woman said, "we are going to send it back to you, it's not exactly what we were looking for after all". Mind you, this was a custom-made vase in the $300 range, and I don't make anything for people to test-drive.
Realistically, I would work with someone to resolve this situation, because I don't want to force someone to buy something of mine that they don't like. But this woman's cavalier attitude was so out of line, and during this time I was still struggling to make ends meet, so her failure to pay me for my work was painful. But I could tell from her attitude that I wasn't going to be able to squeeze a dime out of her. I called up her voicemail and left her a long and scathing message, starting with, "I'm sure you buy a ton of stuff you don't care about and return to the store, but I am not POTTERY BARN!" That was a customer I definitely lost, and I was happy to let her go.