To represent Seller ("Listing Broker"). Dual Agency (§ 18.86.060) – Dual agency is legal in Washington only if the agent obtains written consent from the buyer and seller. A broker may act as a limited dual agent only with the written consent of both parties to the transaction, set forth in the services agreement. If the Property is sold to a buyer who Listing Broker also represents, Seller consents to Listing Broker and. Supervising Broker acting as dual agents. A listing agreement is a legally binding contract between a homeowner and the real estate agent or broker who will be listing the property for sale. The largest market for a seller listed with an agent is the other agents in the multiple listing service. Open Listing Agreement: This type of agreement allows the seller to list the property with multiple agents.