This is a personality thing. I also can't stand pushy salespeople or salespeople who don't have a clue about what they are selling. In some locations salespeople tend to be more watchful of customers because it seems a very small percentage of those "customers" might walk out of the store with their "purchase" without bothering to stop at the checkout counter.
I have two sons who worked at both West Marine and Boaters World while they were in school. Its incredible the stories they relate about how rude that a precious few customers can be. They both agree that the problems are somewhat related to the ways certain managers choose to staff their stores. It seems that they try to be cost effective, but don't track potential high volume days, like spring weekends, and as a result are understaffed ( like only one salesperson) . Sales get missed because some people who truly need help finding product just can't be waiting around.
Here's another interesting point: Customer flow has changed since Boaters World announced their closing. They aren't happy when they come into a West Store and find little or no inventory for example, in the paint section. They complain about paint prices being higher and blame it entirely on West, apparently forgetting that petroleum prices going through the roof last year might also have something to do with it.
Finally, as a general observation, both of my sons agree that sailors in general are more patient, more knowledgeable, and easier to work with than powerboaters. (One of my sons happens to be a powerboater/fisherman.)