If thats a German made Walther I'd buy it right now for that price, yesterday in fact.
I imagine the S&W ones can be fine, I believe they are backed by their lifetime warranty? I certainly wouldn't be afraid of one.
As to why the Interarms gun wasn't shot much hard to say. One possibility is simply that they aren't all that pleasant to shoot, particularly if you have fleshy hands. They kick harder and snappier than you might think due to the recoil operated system. they also aren't particulary cheap to shoot unless you reload it, which most don't.
Or maybe its like so many guns, the guy just plain didn't shoot much.