Seller Agency is a relationship between a real estate agent and the seller in the brokerage of homes. The listing agent and the seller enter a written contact (the "Exclusive Listing Agreement") under which such particulars as home price, duration of agreement, commission, rights & obligations, duties, etc. are specified.
The listing agreements are most commonly of the "exclusive sale" variety, under which the agent/broker earns a commission even if the seller finds the buyer (in an exclusive agency agreement, the agent/broker must procure the buyer to earn a full commission).
The Listing Agent/Broker owes the Seller full duties as her fiduciary, including honesty, loyalty, dedication to purpose, acting in the Seller's best interests, etc., in exchange for the Seller's agreement to allow the Agent/Broker to sell the property and earn a commission. The Listing Agreement usually specifies that the Listing Agent/Broker agrees to share, 'co-op', or split, the total commission with a Buyer Agent/Broker who represents the Buyer.
These terms are frequently set out in the Multiple Listing Service for the Seller and Listing Agent, and in the buyer listing service for the Buyer and Buyer Agent.