Knowledge and experience are key to successful painting. Reputable painters know which products to use where, drying times, and drying temperatures.
Some painters request large, up-front payments to cover the paint purchase. Avoid up-front payments whenever possible. Some painters spend the advanced money on something other than paint and then delay starting the job because they have no paint. Lending money to a painter who cannot afford to buy paint is a risky proposition. If you must hire such a painter, accompanying the painter to the store to purchase the paint is a good compromise. You should pay the store directly for the paint and then take the paint back to your house. Of course, an even better solution is to hire a reputable company in the first place.