Interesting information! We just got scammed in White Stone, Virginia... we chose the same color, but went from a flat to an eggshell finish. I wasn't available to stand over the painter while he painted. For such a detailed job, I marveled at how quickly he finished the project! After he was paid for the job, we discovered all he did was roll paint across the walls and close to the crown, baseboards and detailed trim around windows and doors leaving about an inch or so of the flat finish. By using the same color, he didn't even do the job he was paid to do, which explained why he could finish the job so quickly. By using the same color... he got lucky and passed it off as a completed job not bothering to paint to and cut in around the trim. Upon further evaluation of our walls we could see exactly where he stopped because we could see the difference between the flat and eggshell finishes. There are walls he didn't even bother to paint. Then where he did paint near the crown when we were in the room watching ... he hit the crown moulding and tried to tell us it was already there... and tried to sell us on painting the crown moulding. I am so disgusted and upset!! He'll be hearing from us to rectify the situation.
A thorough scrubbing is a must before painting any exterior surface. It removes the dirt and broken-down paint residues that keep fresh coats from adhering and gets rid of mildew that grows on paint in all but the most arid climates. Most contractors clean with pressure washers, but in the hands of someone unfamiliar with the equipment, these can gouge wood, shatter glass, and drive water behind siding and trim. Using a hose, a pump sprayer, and a scrub brush is slower but safer, and just as effective.
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.
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.