I guess selling them to legitimate dealers who would in turn, of course, sell them to law abiding firearms owners would make too much sense.
Our local Sheriff has always auctioned guns taken from illegal owners (drug dealers, felons, etc.) to the general public. He puts a notice in the local paper with a list of some of the guns. The auction is usually held at a local church. Background checks are done but no guns are destroyed unless they are dangerous (faulty). I guess that’s the difference between Tennessee and Michigan.