Mich. Comp. Laws § 257.1331: Acts or practices barring action on contract, action for collection of compensation, or assertion of lien; recovery of amount paid unregistered facility.

Sec. 31.

A person who engages or attempts to engage in the business or trade of a motor vehicle repair facility or specialty or master mechanic without a registration or certificate, or engages in an act or practice in violation of this act or a rule is barred from bringing or maintaining an action at law or equity on a contract or for the collection of compensation for work performed or materials or parts provided to any other person. In addition, the person is barred from asserting a mechanic's, garageman's, or similar lien upon a motor vehicle, including the repossession of a motor vehicle. A customer is entitled to recover any amount paid to an unregistered facility for the repair of a motor vehicle belonging to that customer.