It varies from product to product and substrate to substrate. For instance, if you are painting a old door that has a smooth slick surface, you probably want to use a primer and two top coats of your finish product to insure adhesion. A painting company should inform you whether or not you need a primer, or even a bonding or blocking primer, some products are even self priming. It also depends on color as well. Deep colors with lots of pigment often need multiple coats. So ask your painter, and read spec sheets, and/or even call your local paint store if in question.

Even though your paint job looks good now, you want to be assured it stays that way. Nothing lasts forever, but there is a time period that it should continue to look great.

All jobs are different. Be sure that your painter is on the same page. If you don't ask your painter if they are filling picture frame pin holes, and you are not hanging your pictures back, up, you might have extra costs to get the job you thought you were already getting.

I feel most of the major paint companies have their good and not so good products. Whichever company you go with, spend a little extra money for better products. It will be worth it in the end.