Sec. 9. (a) Every owner of a vehicle for which the wheel tax has been paid for the owner's registration year is entitled to a credit if during that registration year the owner sells the vehicle. The amount of the credit equals the wheel tax paid by the owner for the vehicle that was sold. The credit may be applied by the owner only against the wheel tax owed for a vehicle that is purchased during the same registration year.
(b) An owner of a vehicle is not entitled to a refund of any part of a credit that is not used under this section.