I once went into a Michael Kors store and that day I had my LV Speedy with me. A SA came up to me and asked me whether she could help me etc. When I said no, her follow up question was "Is that a real one?". I literally have never felt so insulted in my life and just said "Well, shouldn't you be able to tell?" and walk out of the store almost immediately after that.
Never returned to that particular store either.
Wow! That is so extremely rude. I don't know how I would have handled that!