Answer: The broker should continue to represent the seller and treat the buyer as a customer.
Step-by-step explanation:
From the information given, we are informed that a broker represents a seller and has an office policy of acting as an intermediary, then a sponsored sales agent brings in a buyer who wishes to purchase one of the broker's listings.
Since the buyer wishes to remain unrepresented, then the broker should continue to represent the seller and treat the buyer as a customer.