To solidify this response, we have been in business for over 30 years as a painting contractor. We didn't just paint a couple of houses 25 or 30 years ago, we paint approximately 900-1000 painting jobs per year and operate with 40 professional painters doing commercial, residential and industrial painting. This article on behalf of Angie's List is totally asinine! I was under the impression Angie's List was only carrying "legitimate" contractors with established reputations. This article written is primarily referring to bottom feeding, one man band operations, trying to hustle for a paycheck.
Oh, where to begin? Let me start with 'watered down paint'. 25-50% before the material gets to the site? Impossible. You would basically be painting with water at that point. It would be less of a hassle, and cost, to simply use proper material. You would be forced to apply three coats instead of two, as the coverage would be horrible. Whatever cost you think might be saved in materials would be lost in labor.