Which of the following actions by an agent is mandatory?

The duty to disclose material facts affecting residential property value is mandatory for real estate agents. This obligation stems from the fiduciary responsibilities agents have towards their clients and the necessity for transparency in real estate transactions. Agents must ensure that all relevant information, which could influence a buyer's or seller's decision, is disclosed.

Failure to disclose these material facts can lead to legal repercussions such as a breach of contract or liability for misrepresentation. This duty not only protects the interests of the parties involved but also upholds the integrity of the real estate profession.

In contrast, advising the seller on pricing, showing properties to potential buyers, and negotiating a sale price are important functions of a real estate agent but are not considered mandatory actions in the same way. These tasks may vary based on the needs of the client or the market conditions and may not have the same legal implications as the obligation to disclose relevant information.