Under Michigan law, the Michigan State Police (MSP) are required to publish a list of the firearms that they intend to dispose of each month. Agencies in Michigan are required to turn over to the State Police firearms that have been forfeited or confiscated from prohibited possessors.
The firearms are checked to see if they have been reported stolen. If they have not been reported stolen, the MSP are required to dispose of them. Before they are disposed of, the list of firearms has to be published each month. Owners of the firearms are given 30 days to contact the police to recover their property.
I doubt if many do so; if they have not been listed as stolen, the chances of the owner checking the State Police list each month to determine if their firearm shows up seems vanishingly small.
The MSP have the choice to dispose of the firearms by sale or to destroy them. They have been choosing to destroy them, likely for political reasons and because of bureaucratic inertia. It is hard to see why they would avoid selling them at auction.