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.
Some contractors work on time and material others on a firm contract. I would never hire the former and am leary of the latter. A contractor may low-ball a bid to get the job planning to make a killing on change orders. If you say good morning to them, they charge you extra for that. If the contract is not very, very specific and extensively fleshed out or if they display their change order schedule prominently on top, show them the door.