What must occur for subagency to be applicable?

For subagency to be applicable, the key factor is that one party involved in the transaction must be unrepresented. This situation often arises when the buyer does not have their own agent and the listing broker, who represents the seller, agrees to work with the buyer as a subagent.

In this context, the unrepresented buyer does not have anyone specifically advocating for their interests, allowing the listing broker to step in and offer assistance by facilitating the transaction. This arrangement legally establishes the listing broker as a subagent for the seller while also assisting the buyer, often leading to a dual agency situation where the broker represents both parties, albeit primarily representing the seller due to their sole agency agreement with them.

The other options suggest requirements that are not necessary for subagency to exist. For example, the seller being unrepresented would negate the primary relationship needed between the listing broker and the seller. Similarly, the listing broker's agreement is implied through the agency relationship with the seller, and having a higher commission is not a prerequisite for establishing a subagency relationship. Thus, the buyer's unrepresented status is the crux of establishing subagency, making it the correct answer.