The name and the size of the store dictates how much its employees get paid. The guy at the front check-out register gets paid about the same as the guy in the stereo department. These people are not experts, they have no degrees or certifications, and they certainly don't care about you as a customer. Occasionally you might find someone who actually likes their job, but a person like that doesn't last very long at a big box store, they usually are only working there until they can get a job that pays them what they actually deserve to be paid.
At a small shop, they get business through repeat customers and word of mouth. They are much more inclined to treat you right and sell you what you need (not what they think you need or they think they can get you to buy in 15 minutes or less). Sure there are employees at small shops that only work there so they can hang with their friends...but you can skip around all that B.S. by asking to speak to the owner, manager, or head installer. One of the three will be there and can offer you expert advice on your installation.