Ask companies to include all details in writing. Although that sounds simple enough, too many contractors submit offers such as "paint house for $5,000." A friendly contractor may offer a reassuring handshake and promise that the crew will take care of all the details — starting on time, working every day, cleaning up, etc. That's great, but why not include each point in the proposal? If it's a challenge to get a written description of labor, materials and other details, things will probably get worse when the work starts.
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.