No seller, in any sale subject to this subchapter, shall offer to pay a commission or give a rebate or discount to the buyer in consideration of the buyer's giving to the seller the names of prospective purchasers or otherwise aiding the seller in making a sale to another person, if the earning of the commission, rebate or discount is contingent upon an event that is to happen subsequent to the time the buyer agrees to buy.   [PL 1971, c. 150, §2 (NEW).]