I managed commercial construction projects for many years, have built and remodeled several properties, and never once have I encountered any of these scams. The tone of this article is deeply troubling. The author seems to be saying that ALL painting contractors are inherently dishonest, and that has not been my experience. The underlying advice here is sound: get it all in writing and cover as many contingencies as possible--so pointing out potential pitfalls like coat coverage is helpful. But do that in the spirit of clear communication of expectations, not with the expectation that the person you are hiring will try to cheat you at every turn. Not every contractor takes outrageous advantage of change orders; not every contractor will sneak past necessary preparation and/or repairs. Contractors of all sorts get a bad rap as it is; reinforcing a stereotype with articles written from this point of view just seems unproductive.
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.