From a lady's perspective, just for grins:
I spent decades in various careers that were all service-oriented and had the advantage of being raised by Southern parents who taught and expected strict adherence to manners ("Yes, Ma'am, No, Sir, Please, Thank You") and graciousness. So, when I worked as a stew for TWA, for instance, their training to "keep a smile on your face if it kills you" was a cinch for me, and boy, could I tell you stories about airline passengers who viewed the (now-politically-correct term) CABIN ATTENDANTS as dirt under their feet.
Knowing how great service can turneth away wrath and charm a smile out of some of the meanest grouches, I tend to gravitate towards Lowe's and Home Depot for the same reason some of you mention, mainly the ATTEMPT to make eye contact and to be pleasant and helpful (even if they don't have a clue). Locally owned building supply places in my area fall short in that regard, at least in my experience. Price and selection, of course, are still a close second to my decision to patronize an establishment and purchase the goods.
One thing I could add that always works for me is to involve the manager on duty in a constructive and non-threatening manner. I ask to speak to them when I can't get the information on what I need to find or get my questions answered. I say something like, "Look, I chose your store today and would really like to do business with you, but I need (fill in the blank)." Most managers I've encountered take the extra steps to make sure I'm taken care of, and many have thrown in a discount when I ask.
How I wish more people serving the public understood the importance of ATTITUDE and trying to help. Customers have long memories when they're dissed (or feel that they have been) and there go additional profits for your employer and possible longevity for your job position.