Don't pass judgement on Margaret until you try and book gigs for a DJ for a living. It's a never ending comedy of errors. While there are really good people who book clubs and promote parties, it does seem to be a profession that attracts the incompetent, the criminal minded, and the insane. It sounds like Margaret turns up the Glaswegian fury to 11 at the first hint of trouble, which can be counter-productive. But it's not like she's never had to deal with promoters out to screw her.
The best practice from my observation is that getting a signed contract and a sizable deposit before traveling to perform. That gives everyone a good incentive to make sure things go according to plan. I've also worked with people who want to be paid in full before performing. As long as you (the promoter) knows this ahead of time, there's no problem, and the performer starts his or her set knowing there's going to be no 5AM drama about getting paid. And yes, I've had performers demand their fee up front out of the blue. It sucks, but on the promoter side, sometimes you have to be flexible. The Tres Manos story kind of bothered me that way, because it violated the first rule of show biz: The Show Must Go On. Even if Margaret was unpleasant, Rolando was there, his name was on the flyer, and he should perform and get paid.
