I've seen this done many years ago by a guy who did all sorts of jobs where I lived. My dad caught him painting his boss's roof and he was watering down the paint. We've had a hard time trying to get a painter for our house. We've had a guy that had been remmended by a neighbor and he hasn't showed up to paint for 2 weeks. I want to call him and my husband says no. I'm 69 years old and I'm about ready to go and paint our 2 porches, I've painted all my life and all the inside of our home. Maybe that's the way it should be with everyone that can paint pretty good.
If you decide to paint multiple rooms in your home, choose colors that relate to one another without being completely the same -- unless uniformity is your goal, of course. Costs may vary based on differences in color, gloss and room size. However, each room will flow depending on the trim's color -- which should all be white or neutral -- so they look connected. A whole-house color scheme presents the same cost factors as painting multiple rooms individually: colors you choose, the gloss, the size of the rooms and time/labor. You can choose to use the same color throughout your entire home to save on money, or you can use a color scheme with the same gloss throughout, though this isn't recommended for selling purposes.
If the point of hiring a well established, experienced, reputable painting contractor is to secure the professionalism and trust suggested to be inherent with that choice, then I would EXPECT that professionalism and experience to include the ability to make the proper and correct calculations for labor and materials for a fixed price quote, and there should be NO reason for the contractor to put the cost burden of their miscalculation on the consumer.
His team is very meticulous, very careful, very clean, and very courteous! They're also very accommodating. For instance, I mentioned a couple spots under some angled siding where I thought a little extra filling was needed, and they obliged without question. Same thing with a request for a stain-proof primer under a balcony. Doing these kinds of little things without question or extra charges is really nice!