I imagine its along the lines of "permissive use" - Unfortunately Michigan lawmakers didnt see FAR enough out to carve out the aspect of "service related" use.
So as the law is written, you hand your keys to ANYONE - person or business employee- you CAN be sued personally.
After being intrigued by this, Michigan is a "no-fault " state meaning normally the only time you can be sued ( by an injured 3rd party ), is if found "legally liable". And it just so happens that the current LAW, as its written, MAKES HIM LIABLE.
Its one of the most insane laws i think ive seen in my 27 years of commercial insurance.