Now the bad news, he said that it had been re-nickeled, and badly at that. Some of the gunk was actually nickel plating that had gotten into the "guts" of the pistol. He said that for $150 I got a great deal but it would not be worth as much on the collectors market because of that.
This is a good time to mention that a good way for a n00b to readily identify a reblued or renickeled modern S&W revolver is to look at the trigger and particularly the hammer. They normally have a color case hardened finish, which appears dull grey with bluish or greenish splotches (look at the M&P in Kamerer's post). The triggers were sometimes hard chromed at the factory, but the hammer should be color case.
A blued hammer and trigger, or a shiny nickeled hammer, are surefire indications of a cheapo refinish job.