You are referring to what they call a "Hold over Clause" which protects the brokerage firm from sellers who try to get a buyer to submit his offer after the expiry date on the listing agreement and he the seller will split the savings on the commission saved. The aforesaid clause only covers instances, where the property was introduced to the buyer during the listing period and resulting from the efforts of the agent. A real estate For Sale sign that alerted the buyer that the property was for sale is sufficient proof of the agents efforts. In litigation, the buyer is asked under oath,"How did you know the property was For Sale" and the buyer replies "I saw the For sale sign. The seller now has to pay the commission, plus legal fees and disbursements. But, if the seller doesn't mind being sued and can prove that the buyer was obtained "solely" throught the efforts of the seller, then no commission will be payable.