Every paint company offers two or three grades of paint products. The "consumer" grades are usually the best products and the "contractors" grades are usually the more inferior products. I use only the highest grade products that are available. There are two reasons for this. One, the highest grade products are not only going to last longer but they are easier for me to work with. And two, I usually get a better price for the higher grade products than I do the cheaper ones.
Most paint stores give contractors their price breaks according to which products they use the most of. The more you use a certain product, the better pricing you get on that product. Since I have always used only the best products available, I actually get a better price for those products than I would the cheaper products because I never buy them.