I am not a lawyer, but I do serve as the Chairman of the Grievance Committee for the Greater Boston Association of REALTORSÂ®. The short and simple answer to your question is that clause 3c) cannot be enforced (see Tristamâ€™s Landing, Inc. v. Wait, in which the MA State Supreme Judicial Court adopted the following rule. When a broker is engaged by an owner to find a purchaser, the broker earns a commission when: (1) he produces a purchaser ready, willing and able to buy on the terms provided by the owner; (2) the purchaser enters into a binding contract with the owner to do so; and (3) the purchaser completes the transaction by closing title in accordance with the provisions of the contract.)
Your listing agreement may have allowed the agent to "carve out" a period of time for someone who was shown the property during the original listing period to enter into a contract with you. Your new listing agent would need to receive a list of any such names in order for the first broker to establish a fact pattern of procuring cause during the listing period. Other than this, you typically have no other duties or owe anything to the first listing brokerage once the listing period has expired, and would be free to enter into a new listing agreement with another brokerage.
I see that your link has Brookline in the url. Our office is in the heart of Coolidge Corner, and we had an office in Wellesley Hills for over 5 years. I'd be happy to assist if you have any further questions.