One of the things I mind about being a writer, and one who gets paid for it, is that sometimes the business side of things rears its ugly head. I don't want to be a business owner, though in a way I am, and in part it's because I don't have the skills for it. I know self-employed owner/operators, and have seen how the good ones work. I don't have it in me. Especially the people skills.
Sometimes, though, I don't get a choice.
Most of the people I write for are also professionals. They may be contracting my creative services (and writing is a creative process even when it's nonfiction- but that's a whole other entry) but it remains a contractual, professional relationship. I expect to be paid if I do what I am asked, especially if I go above and beyond what is initially asked. Which I might do if the request is reasonable and the person nice enough about it.
But there are those people who don't quite grasp the concept that I do this to get paid. Granted I write for other reasons, but very, very little of anything I've ever written for a paycheck was something I'd have just sat down and wrote without the dollar signs - however few in number they may be - hanging in front of me. Not everyone comprehends that, and the worst are generally those that are putting together some sort of project. Worst still are those for whom the project is either personal or some sort of pet project - and that doesn't have to be an individual, it can be a non-profit or something else, though most of the time the ones I have trouble with are the individuals.
These are the kind of people who think that because it's a labor of love for them, it must be for you, the writer, too. They also seem to think that it's no big deal if they don't pay you what they agreed on, don't pay you on time, or try simply not to pay you at all. One such entity offered me a tax deduction because it was non-profit. (Like those help me much. I need the paycheck, especially in this economy.) These are also the people with whom, eventually, you have to revert to business mode.
Where you play nice, be polite, and then go for the jugular when they don't get it right the first time.
... And then write grisly deaths for them in the next WIP. ... After you've been paid.