Here is my take on the paint dealer vs home center, and anyone is welcome to disagree. I have established a long-term relationship with a paint dealer, based on their ability to provide top quality products, useful information, advise and accessories not found in home centers. They also keep track of what I buy and make appropriate suggestions. They let me try out new things risk free and accept returns on things that don't work out. I receive discounted (contractor) prices even though I am not a pro painter. As a result their prices end up slightly higher than discount home centers. However, I have bought paint at both places, and have disposed of a great deal more paint from the home center that was not the quality or finish I had hoped for, and I have learned that cheaper paint generally does not pay due to needing more coats / time to apply.
In return for my patronage, the store makes an effort to ensure my satisfaction and retun business. They know what projects I am working on and ask how the kids are doing. I like that. If cost is your bottom line, it is unlikely you will go to the paint center. But if you develop a patronage, I doubt you would go back to discount.