Payment. Every client is different. Every job has it's own unique set of circumstances. I always start off the discussion with my clients saying that I'm flexible on how they would like to proceed with payments but that I prefer half down. I refuse to change order. Change orders are my last resort. Instead I ask questions at our initial meeting and try to be sure to cover all bases before I submit my estimate.
I used to work at Sherwin Williams. The best thing to do is specify that you will purchase your own paint. If the painter objects strenuously, he was plaanning on making money in the ways this article outlines. You might pay a few dollars more for paint, but you will have control of the quality of what goes on your walls. Never skimp on paint quality.