REALTORS® Code of Ethics: Duties to Clients and Customers, Article 1, Standard of Practice 1-8

REALTORS®, acting as agents or brokers of buyers/tenants, shall submit
to buyers/tenants all offers and counter-offers until acceptance but
have no obligation to continue to show properties to their clients after
an offer has been accepted unless otherwise agreed in writing.
REALTORS®, acting as agents or brokers of buyers/tenants, shall
recommend that buyers/tenants obtain the advice of legal counsel if
there is a question as to whether a pre-existing contract has been
terminated.

See entire Code of Ethics HERE