I would buy pre-owned jewelry from a reputable source, and would not care if it was lucky or not. Since you love it and felt that it was a good deal, that's all that matters. Depending on the stone size and amount spent, I would ask the store for some type of certificate or statement stating the color, clarity, cut, and carat, and would consider getting it appraised elsewhere for piece of mind.
I would definitely recommend that you do this! I think it's customary that if you spend more than $500, you should get a certificate, especially when it's a diamond.
If you want any more info that I can give you on the price or colour clarity etc you can feel free to PM me
