The retail dealer shall be held responsible for the quality of the petroleum products he sells or offers for sale: Provided, however, that the retail dealer shall be released if the results of analysis of a sealed sample taken in a manner prescribed by the Commissioner of Agriculture at the time of delivery, and in the presence of the distributor or his agent, show that the product delivered by the distributor was of inferior quality. It shall be the  duty of the distributor or his agent to assist in sampling the product delivered. (1937, c. 425, s. 18; 1949, c. 1167.)