Bought the center stone for my wife's engagement ring from a wholesaler I knew at the time. It's a certified diamond so really good quality with pedigree, then bought her ring from a retailer and had them set the stone. After I had it appraised, turns out it was worth 3 times what I put into it.
Bad purchase? Not really a bad one, but I sold some stock during the recession to put a downpayment on my house (first home and no equity) so I took a horrible hit on value. Many years later, I'd have done things differently but I guess that's how we make our way. Still have the home, and whatever money was lost in the stock sale has come back two fold, so long term not too bad.