Which of the following must be included in a valid listing contract?

A valid listing contract must include a definite expiration date to ensure clarity and commitment from both parties involved. This date establishes the period in which the real estate agent is authorized to represent the seller and attempt to find a buyer for the property. Without a specified timeframe, both the seller and the agent could face confusion regarding the duration of their agreement, which may lead to potential disputes or misunderstandings.

In the context of a listing contract, including an expiration date serves several purposes: it provides a clear timeline for marketing efforts, it allows the seller to reassess their strategy if the property does not sell within the specified period, and it protects the agent from being indefinitely bound to a contract without further engagement.

The other options do not align with the fundamental requirements of a listing contract. Personal financial information or a buyer's intentions are not necessary for the contract's validity, and appraisals, while useful in pricing, are also not a mandatory component of the listing agreement.