Regretted purchases? At the time, I regretted buying a 6" Smith Model 29-2 and 4" Smith Model 25-? (around 1990) as I had no interest in either caliber. Bought them because a friend needed the money. Didn't shoot either. Sold both of them within about 3-months. Now, as I see the interest in both of these guns, I regret selling them off. But you can't have one of everything, or at least I can't. At the time, I had no regrets.
Truly regretted purchases are the ones that I bought as collector pieces that I didn't take the time to really look over carefully. One was a reblue, well done, but reblue all the same. They tend to leave a sour taste in my mouth, but life goes on. Usually sold them first chance I got. The problem here is knowledge. I can't or won't mis-represent a gun and have someone else go through the same feelings. To be truthful about "regrets", I have few. Or...maybe not buying more.... more!