In many states real estate law requires an agent, whether in an "agency" capacity or not, to disclose material facts to their client. Material facts are those that, if known by the buyer or seller, might influence them to change their purchase or sale actions.

In addition, the fiduciary duty of disclosure would include just about any knowledge the agent has that might benefit their client in the process of the real estate transaction. For example, an agent working for the buyer, under a buyer brokerage agreement, who is aware of the fact that the seller is in financial difficulty and highly motivated, should disclose this fact to the client,  to help him/her with the negotiation.