In England, little is known of the trade and its structures before the late 13th century, at which paint guilds began to form, amongst them the Painters Company and the Stainers Company. These two guilds eventually merged with the consent of the Lord Mayor of the City of London in 1502, forming the Worshipful Company of Painter-Stainers. The guild standardised the craft and acted as a protector of the trade secrets. In 1599, the guild asked Parliament for protection, which was eventually granted in a bill of 1606, which granted the trade protection from outside competition such as plasterers.
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.
This job is usually done by a professional house painter. The painter will assess the walls, clean, and make any necessary repairs or removal of old wall coverings. They will also tape off any adjacent surfaces and cover nearby furniture and floors with drop cloths. Typically, they will apply a layer of primer, then one to three coats of paint, depending on the color and coverage. Once the paint is dry, they take a final walkthrough to inspect and make any necessary touch ups. House Painting Westminster Colorado