I've heard similar stories from people who carry vintage bags into boutiques. Most SAs, even in the boutiques, don't stay around long and often aren't fans of the designer/design house. They know what they have to sell (mostly) and very little outside of that.
That said, it's NEVER appropriate to treat customers badly, either out loud or by your actions. SAs not helping customers because they assume someone doesn't have money based on how they're dressed is a similar sort of thing. It's just stupid, and it loses SAs a lot of sales. More than they realize, probably. (My best story in that vein involves Xavier Roberts, the guy who created Cabbage Patch Kids, and a car salesman.)