REALTORS® Code of Ethics: Duties to Clients and Customers, Article 1, Standard of Practice 1-7

When acting as listing brokers, REALTORS® shall continue to submit to
the seller/landlord all offers and counter-offers until closing or
execution of a lease unless the seller/landlord has waived this
obligation in writing. REALTORS® shall not be obligated to continue to
market the property after an offer has been accepted by the
seller/landlord. REALTORS® shall recommend that sellers/landlords
obtain the advice of legal counsel prior to acceptance of a subsequent
offer except where the acceptance is contingent on the termination of
the pre-existing purchase contract or lease.

See entire Code of Ethics HERE