One thing about a used gun you never know and must accept as possible, some yahoo might have trimmed the hammer spring to lighten the DA trigger. That can cause light strikes. Not a big deal at all to fix, though.
I've got two M66s, one was 197 bucks, the other 180, both bought at gun shows. The $197 one is cherry, nickel finished, fantastic shape. The other is the older lockwork blued gun. I wanted it for the 3" barrel length for carry. It had a timing problem I used to bargain the price down that didn't cost me anything other than some head scratching and taking the side plate off to figure out. Been shooting tight groups with it ever since.
That's one thing I love about the Taurus revolvers, genuine high quality guns for very low prices. Seems like the older a Smith gets, especially with all the griping about locks and MIM parts from the purists, the more expensive they get! I saw a decent Ruger Security Six 4" stainless gun like the one I used to own the other day going for $400! I'm a shooter, not a gun investor. I like to buy quality at low prices.