Buy IT
ANY used S&W revolver for $300 would last MAYBE half a day in the gun case of any of my local dealers here in PA. I don't know what it is, old Smiths are few and far between and those in any kind of shootable condition fly off the shelf for even more than $300. A 13, even if someone didn't know exactly "what it was" would sell for $300. Not to knock the K-Frame .357's, but my fear with buying them used around me, is that some goober might have not known any better and fired a few thousand hot handload .357's "Same as I use in ma Ruger huh huh huh!!" and loosened it up. They just see that ".357 Magnum" on the barrel and think they can blast away with the hottest stuff they can crank out of the Lee press.
I snapped up a cosmetically beat and carelessly handled,but lightly fired 10-5 6" for $270 and the owner said "good move, some guy said he was coming back for that tomorrow, he had no cash on him". Gotta buy em when you sees em I guess!
I had seen a 4" Model 19 for sale in another store near me for $375, that was two months ago so it's a pipe dream to think it's even still there. Next to it was a Bernadelli 9mm auto that has been laying there for 3 years.
Meanwhile there has been a 6" Colt Official Police in fair but solid shape sitting there for a year for $350, the Colt's just don't sell as much, that's why I was able to get a very nice Positive for like $250.