Rescission:
When a breach of fiduciary duties by a real estate agent is involved, the principal can ask the courts to rescind the contract and restore them to their status before entering the agreement. This could involve return of the property to the seller and refund of the purchaser's money. There does not need to be something unfair about the transaction itself, only the breach of fiduciary duties by the agent.
Forfeiture of Commission:
No payment is entitled to a real estate agent that breaches their fiduciary duties. Thus the agent can be required to refund any compensation received.
Damages:
A breach of fiduciary duties by a real estate agent could result in damages to their client principle. If so, the agent would be required to compensate the client for those damages. Suppose the agent for the seller of a property failed to present a better offer to the seller than the one they accepted. The agent would be required to reimburse the seller for the difference in the lower and higher offers.