Mich. Comp. Laws § 445.1406
A person shall not charge, collect, or receive from a buyer, directly or indirectly, any further or other amount for costs, credit investigation charges, insurance premiums, examination, appraisal, service, brokerage, commission, interest, discount, expense, fee, fine, penalty, or other thing of value in connection with a home improvement installment contract, home improvement charge agreement, or home improvement charge sale, other than the charges authorized by this act. Any such unauthorized charge shall be unenforceable. Any payment of an unauthorized charge shall be applied to the next maturing installment, or, if a contract has been fully paid or a balance is not owing under an agreement, shall be remitted to the buyer and the buyer shall be entitled to recover all such unauthorized charges.
MCL 445.1406