So why not just paint your own home. I'm not a painter, so my wife and I take our time, buying the paint and supplies, and doing our own painting. Yes, we need to tape, and it's not perfect, but we get the satisfaction of seeing our completed work. Get the supplies, sliders for your furniture, and patience and go for it. That way YOU have control over the entire project.
The other difficult part is getting a painting contractor to show up. While this generalization does not apply to every painter, personally I am extremely grateful if I can get a paint contractor to show up to look at the house and to later produce a written estimate. I hardly fault the painting contractors, because I think it is a combination of the contractors being smaller operations along with a high demand for their work.
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.