As you walk through your lighted rooms (preferably day light) see if the new coat has light spots showing the precious paint. This is call "bleeding through". This means that there's only one coat of paint or the paint was diluted or the trasition of colors were from light to dark (or the other way around) and primer was not use or the painter is inexperienced.
To solidify this response, we have been in business for over 30 years as a painting contractor. We didn't just paint a couple of houses 25 or 30 years ago, we paint approximately 900-1000 painting jobs per year and operate with 40 professional painters doing commercial, residential and industrial painting. This article on behalf of Angie's List is totally asinine! I was under the impression Angie's List was only carrying "legitimate" contractors with established reputations. This article written is primarily referring to bottom feeding, one man band operations, trying to hustle for a paycheck.
If you paint over dirty, oily surfaces, the paint will easily chip or peel off. So before painting, clean grimy areas with a deglosser or heavy-duty cleaner intended for prepaint cleaning. They work well to clean painted, varnished or enameled surfaces to improve the adhesion of the new paint. They’re ideal for cleaning greasy or oily areas like kitchen and bathroom walls and removing hand marks around light switches and doorknobs.
Back to the article. You can add water to all latex based paints / thinner to oil based paint. The tinting base has absolutely nothing to do with it. Say you are working outside and throughout the day you have to add a little water to keep the same consistency. If somebody really tried to add 20% to 50% water they no longer would be painting they'd be performing a whitewash or pickle finish.