Wear is just what you see: rust, scratches, bluing loss, damage - from being dropped, or modified, or poor repairs, etc.
In addition, the lockup, timing, forcing cone, and barrel should be checked. Here's a good reference. http://www.thefiringline.com/forums/...threadid=57816
Does it have the box and papers? How about the original grips? What dash # is it? All of these things affect the value of the gun. IIRC, the 19 no dash through 19-4 had pinned barrels and recessed cylinders and are the most desired. Additionally, any barrel length shorter than 6" is more sought after than the longer barrel lengths.
The 19 was a fine 357 which should be fed a steady diet of 38's and on special occasions 357's. If it checks out ok and you can get it worth the $$, buy it! You wont be sorry.