Where any road vehicle is loaded with goods for sale by weight to a single buyer of the whole of the vehicle’s load, or for delivery to the buyer after they have been so sold, the buyer or seller of the goods, or any inspector who shows that he is authorised so to do by the buyer or seller of the goods, may require the person in charge of the vehicle to have it check-weighed, and if that person fails without reasonable cause to comply with any such requirement he shall be guilty of an offence.