I do not know off hand if it's just a hammer replacement to convert a DA only gun. I would definitely want a gun capable of single action as well as double action fire. It is more practical, and would probably be worth more if you decide to sell down the road. I would also look for a gun with adjustable sights, such as a model 19, 66, or an L frame 586, 686. POI can vary, depending on the gun and load you are using, and the adj. sights are a nice feature.
You want to make sure the timing is good (cock the gun slowly, while keeping a little drag on the cylinder, it should lock up. If not, and it takes a little extra push for it to lock, then most likely the hand is worn, and needs replacing). Also check the lock up feels tight, without a lot of slop, or front to rear movement of the cylinder. Test the trigger pull both SA and DA, they should be smooth, without any binding. Same with the ejector. Check the bore for rust and pitting.
I would not be overly concerned with the exterior finish on a "shooter" grade gun. A lot of ex-service guns show a lot of finish wear from the holster and weather, but are tight mechanically, having not been shot very often.
Earlier guns with pinned barrels and recessed chambers tend to bring a little more money to collectors. Later models of these same revolvers without those features are just as strong, and bring a little less $$. In today's market, a good shooter grade K or L frame Smith is bringing, very roughly, about $350 / $450. 98% examples, complete with original box and accessories can bring $700 or more, depending on the model.
Larry