It totally depends on who's asking. One time a friend of mine said "I'll give you a hundred bucks for that diamond necklace you have on". He totally believed it was real. I said "OK" and started laughing. I told him it only cost me 60 and it was fake. We had a good laugh.
I live in a small town and everybody knows everybody. So if it is someone that thinks they are uppety up, I don't tell them. If it is someone that doesn't have much or a customer of mine, I tell them! I don't want to think I'm getting that rich from my store.
My family probably already knows and doesn't have to ask!