(e) Nothing contained in this subsection shall prohibit a manufacturer or distributor from offering or providing incentive benefits or bonus programs to a retail motor vehicle dealer or prospective retail motor vehicle dealer in this state who makes the voluntary decision to offer to sell or sell any extended service contract or extended maintenance plan offered, sold, backed by or sponsored by the manufacturer or distributor to sell, assign or transfer any retail installment sale or lease by him in this state of motor vehicles manufactured or sold by the manufacturer or distributor to a specified finance company or leasing company controlled by or affiliated with the manufacturer or distributor. Any statement, threats, promises, acts, contracts or offers of contracts, when the effect may be to lessen or eliminate competition or tend to create a monopoly, are declared unfair trade practices and unfair methods of competition, against the policy of this state, and are unlawful.