Constantly! In my case, I do work in retail, so many people probably have me filed in their minds as a retail associate, but haven't got the specific store right. It happens so often that I probably sound irritated when I tell them that "I don't work here." What irritates me is when they assume I work there instead of asking me if I do.
This reminds me; I just saw the Big Bang Theory episode in which Sheldon is at the Electronics store and ends up spending a long time solving everyone's computer problems. An employee of the store ends up pointing out to Sheldon the he doesn't work there when he sees Sheldon using their computer terminal to help another customer.
I'm sorry, but I don't remember his response, but it would be funnier anyway if you find the clip and hear it from him.
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