Where transportation is involved in the sale of personal property and the price at which such property is sold is determined f.o.b. shipping point, the consignee may determine the means of transportation to be used and the routing of the shipment, except that if the consignor has not received written shipping instructions from the consignee designating a specific carrier a reasonable time prior to the making of the shipment, the consignor may determine the means of transportation to be used and the routing of the shipment.