Have to be a mite careful also with those who talk the talk. There's an S&W specialist (overgrown pawn shop!) on the web who will measure every aspect of a copshop tradein. They'll tell you the B/C gap is .005 in the first para and .009 in the next. The top strap can be half torched thru and they'll tell you gas-cutting is at an acceptable level. They'll tell you (in degrees of arc) that the cylinder locks up before letoff. I should hope so! There are better deals to be had from folks who know even less than you or I.
jack