I've been coming here for my painting needs for the last year. I've finally had it with the big box stores.
First of all, the service is top of the line here. The store staff knows their stuff and is eager to help the DIY folks as to the proper paint and equipment to use. One thing I learned was to purchase a 5 gallon bucket and attach a metal screen inside the bucket to roll your paint brush into instead of that small flat paint trays. Using the bucket with the metal screen makes the job go much faster. The big box store has a metal screen made in china that constantly detaches from the bucket. The Sherwin Williams screen stays on the bucket. You DIY painters will understand what I'm talking about.
So you get what you pay for, quality and materials at a Sherwin Williams versus the cheapest materials and sketchy service at the big box stores. The choice is yours.