These stories are a pet peeve of mine.
This goes back to basic pride in your work. Some people have it but most, unfortunately, do not. When I was a kid I bagged groceries, worked fast food, changed oil in cars, etc and I always made it a point to know what I was doing. I don't care if someone works at Dairy Queen, Macy's, Tourneau, or an Omega boutique they should know more about their products than 99.9% of the customers. It's not 100% because there will always be that one guy, sales people get a pass dealing with him. The rest of the time there is no excuse.
I currently have a full time job and two part time gigs that I work around my Army schedule. I have made a point of taking the time to learn all of them. How is it that a salesperson at a watch counter at a department store cannot? In my chosen profession, US Army Infantry, people not knowing their trade don't get themselves killed, they get people like me killed. The dumb seem to always come out unscathed. I suppose that is one of the reasons these situations make me angry but honestly, I have always felt this way.
I try to not be a jerk to ignorant sales people depending on my mood and how much I feel that they are at least trying. One thing that I have begun to do is write letters, not emails, to managers as well as corporate headquarters, and the product manufacturers to notify them of a poor CS experience due to ignorant staff. To be fair, I have also written letters praising people that deserve it. While to some, it may not seem worth the effort, it has gotten me quite a few responses as well as discounts and a bit swag here and there. More importantly though, my goal is to get the dead weight out of there and get people in that have the self respect to do a proper job.
Edit: Thanks to the OP for pointing me to Frederique Constant. They were not a brand that I had ever really looked into but I like what I see. I'm just not going to get one from Bloomingdale's...