Any threat, express or implied, made to a retailer by a manufacturer that the manufacturer will cease to sell, or refuse to contract to sell, or will terminate a contract to sell, motor vehicles to the retailer, unless such retailer finances the purchase or sale of motor vehicles only with or through a designated person or class of persons or sells and assigns the conditional sales contracts, chattel mortgages, or leases arising from his retail sales of motor vehicles only to a designated person or class of persons is prima facie evidence that the manufacturer has sold or intends to sell motor vehicles on the condition or with the agreement or understanding prohibited by this chapter.