Whether or not you are contractually obligated to pay real estate commissions for the listing of your property for sale after its lisitng expires is determined by the written listing agreement that you would have had to sign under regulations by your state's department of real estate.Read your listing agreement carefully in that its terms and conditions control the obligations owed to you by the listing brokerage and vice versa in the absence of conflicting state law. Most likely the listing agreement has a provision that any party who looked at the property for sale and who later purchases it even after the listing expires entitles the listing agent to real estate commissions if the sale closes.