this lookslike a job for gp100man! no really, just check the top strap real good. the part thats just above the forcing cone sticking out of the breach end of the barrel but of course you know that. Id try to negotiate for $50 myself since its used. While checkiing it out lock it up on each chamber making sure its acceptably tight on each one, check the pin and all that you should be good to go.
for the record my 2012 6" was exactly $600.