Final answer:
The broker should inform the seller about the post-dated check associated with the offer, ensuring transparency in the transaction.
Step-by-step explanation:
When a buyer presents a post-dated check with an offer, the broker should inform the seller as to the form of the deposit. This is a critical step as it provides full transparency regarding the terms of the transaction, including the payment to be made at a future date specified in the check. By doing so, the broker ensures that the seller is fully aware of the details concerning the buyer's offer and can make an informed decision about whether to accept it, seek a guarantee of funds, or negotiate alternate terms.