Which of the following is a requirement for a broker to collect a commission from both parties in a transaction?

To collect a commission from both parties in a transaction, it is essential for the broker to have knowledge and consent from both parties. This requirement ensures that all involved parties are fully aware that the broker is representing both sides and that they agree to this arrangement. It protects the interests of the clients by ensuring transparency and preventing any potential conflicts of interest.

When both parties provide their knowledge and consent, it establishes a clear understanding regarding the broker's role and the commission structure, fostering trust in the transaction process. This practice aligns with ethical standards in real estate, which emphasize clear communication and informed decision-making.

The other options do not adequately fulfill the legal and ethical requirements needed in such scenarios. For example, relying solely on verbal consent may not provide enough documentation or clarity to confirm the agreement. Insufficient contact with one party does not establish a legitimate basis for a commission claim, as it could lead to misunderstandings about the broker's representation. A written contract detailing the commission is certainly important, but without the mutual consent and understanding from both parties, the broker may not have the right to collect commissions from each side effectively.