The gasoline and oil inspectors shall pay at the regular market price, at the time the sample is taken, for each sample obtained for inspection purposes when request for payment is made: Provided, however, that no payment shall be made any retailer or distributor unless said retailer or distributor or his agent shall sign a receipt furnished by the Commissioner of Agriculture showing that payment has been made as requested. (1937, c. 425, s. 15; 1949, c. 1167.)