I did a lot of shopping around. I cannot handle the idea of overpaying for things. I guess it makes sense since I make a living out of buying things I deem to cheap and selling things I think are dear.
After doing all my research, I was prepared to spend ~$15k and had located the ring my wife liked most and decided to buy it from Tiffany & Co. I went in there and thought I could get a ring that was listed at $17k for $15k. Turns out they don't negotiate. (Winston and Graff do, FYI). Then I looked on eBay to see what kind of discounts there were to be had on rings from failed engagements / marriages. There was value there, but I the market was too transparent and people seemed to be overpaying considering things were used. I needed to find something that was less well advertised. So I started doing Craigslist searches via an aggregator. I found the exact ring style and size I was looking for but better quality. It was in LA from a divorcee and listed for $11k plus the matching band for $1k (the matching band was ~$2.5k at Tiffany). I had some Jetblue points and flew to LA, met her at Tiffany in Beverly Hills where they determined it was legit. I bought the ring and the band for $10k in total.
So what I got was Tiffany & Co., 1.17 ct, round cut, E, VS, GIA cert, Tiffany papers, with accompanying diamonds flanking the center stone in a channel-set band, plus matching wedding band w/ channel set diamonds. Quality pieces.
I was 23 at the time (2007), so I was tighter with $ than I am now, but I would still do the same. I don't think I got a screaming deal, I just felt satisfied that I paid less than others (if I had went to Tiffany & Co., I would have paid $18k for this ring as it was better than the one I was looking at for $17k, and would've paid $2.5k for the band, and then 10.25% Chicago sales tax at the time = $22.6k). So I avoided spending an additional 12k (which I wouldn't have done anyway, but still).