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.
Some proposals simply say to paint the walls and ceiling and never specify the number of coats to be applied. If the colors are similar enough, it's possible to get away with one coat of paint and not discount your pricing. No matter how hard you try, tiny, pin-sized air holes will pop exposing the original walls. This may not bother you if you can't notice it, but principally speaking you should have paid your painter less for the work.