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.
Also, don't be afraid to ask if the painters are trustworthy people. Unfortunately, there are plenty of cases where a painter has stolen items from a home or caused damage to the house or injury to the homeowner. Subcontractors may not be as skilled as employees, and the contractor you're hiring may not have much experience working with them, making them more of a risk. Additionally, ask if the painters are employees or subcontractors, and what the screening or hiring process is like. If the company conducts background checks, that's a good sign.
My husband has been a professional painter over 30 years. He prides himself in his high level of work ethic and customer satisfaction. He stays up to date on techniques and finishes. He gives Very detail and accurate appraisals with contracts. At an alarming rate, as he starts to finish the last day or the day before, the client starts nit picking and being disrespectful towards his work when every day prior to that, they were very pleased, as he request ongoing satisfaction throughout the job. Then they don't to want pay remaining balance, bicker about final cost, or stop payment. He has a crew he has to pay whether the customer does or doesn't honor the contract as well as our own household expenses. Wasted time ,labor, money and effort lost. Now how do we fix this? Remind yourself and clients that a contract is based on honor.