Safest way to ensure that everything is fair is to get it ALL in writing , signed by both parties. Specify each item that needs repair. Also, BUY the paint YOURSELF. That way, there is no incentive to water it down, and you KNOW that you are getting the grade/quality you actually purchased. Don't be penny wise and pound foolish; if you are paying to hire a painter, buy the best paint that you can afford, to ensure maximum life of this home improvement.
Enforcement of this Act by the Painter-Stainers Company was sought up until the early 19th century, with master painters gathering irregularly to decide the fees that a journeyman could charge, and also instigating an early version of a job centre in 1769, advertising in the London newspapers a "house of call" system to advertise for journeymen and also for journeymen to advertise for work. The guild's power in setting the fee a journeyman could charge was eventually overturned by law in 1827, and the period after this saw the guild's power diminish, along with that of the other guilds; the guilds were superseded by trade unions, with the Operative United Painters' Union forming sometime around 1831.
Some contractors work on time and material others on a firm contract. I would never hire the former and am leary of the latter. A contractor may low-ball a bid to get the job planning to make a killing on change orders. If you say good morning to them, they charge you extra for that. If the contract is not very, very specific and extensively fleshed out or if they display their change order schedule prominently on top, show them the door.