rWt,
I think you're referring to Smith and Wesson revolvers. He made it clear he's looking for a Detective Special, which was made by Colt.
gator,
There's a very well-worded sticky at the top of this forum by Jim March. Review it and you'll be armed with a good amount of knowledge. Colts are unique in that they lock up as the hammer comes down when the trigger is pulled. When evaluating the lock-up, ease the hammer down, and with the trigger completely to the read the lock-up should be tight. Grasp the cylinder and try turn it to the left and to the right. You should not be able to feel any perceptable "slop" with the hammer down.
Those older Colt's are great guns. I have two newer Colt D-frames, a Detective Special and a Cobra. When I went looking, had I found an affordable D-frame from the older generation of Detective Specials I would be owning two of those instead. I much prefer the sights on the older generation to the newer one, and many feel that the triggers on the older generation are superior.