For me looking around the FS ads its simply price. Most of the items I am interested are nearly the same price as it would be new. Its not my preference to buy a used handgun for $50 less than the same model is new.
I very rarely see those "good deals" in the items I am interested in.
One thing to consider is that generally it's not just $50 less than new retail. It's 50 dollars, plus ffl, plus tax or shipping. And unless a gun has been in one of our famous floods or used as a hammer or lever of some sort, used is typically not an issue.