Two defined triggers decide when the agreement is needed, and both are narrower than they sound. NAR's own guidance explains that "working with" a buyer distinguishes participants who provide full or limited brokerage representation or services for the buyer, such as identifying potential properties, arranging for the buyer to tour a property, performing or facilitating negotiations on the buyer's behalf, or presenting the buyer's offers, from participants who simply market their services or just talk to a buyer, as at an open house. A participant working only as an agent or subagent of the seller is not working with the buyer, and needs no agreement with them.
"Touring a home" means the point at which the buyer, or the participant acting for the buyer, enters the house, and it expressly includes a participant entering a home to give a live virtual tour to a buyer who is not physically present. A home for this purpose is a residential property of not fewer than one and not more than four dwelling units. The agreement can be signed at any earlier point, but no later than that.
The four required terms, and why the third one is the important one. A written buyer agreement must contain a specific and conspicuous disclosure of the amount or rate of compensation the participant will receive, or how it will be determined, to the extent the participant will receive compensation from any source. It must state that amount in a manner that is objectively ascertainable and not open-ended. It must include a term prohibiting the participant from receiving compensation for brokerage services from any source that exceeds the amount or rate agreed with the buyer. And it must carry a conspicuous statement that broker fees are not set by law and are fully negotiable.
The third term is the one worth understanding before signing, and it is reported least. It makes the agreement a ceiling rather than a disclosure. If the buyer agrees a figure and the seller separately offers the buyer's brokerage more than that, the excess cannot reach the agent under the agreement. That closes the arrangement in which a buyer's agent's pay rose with whatever the listing side chose to offer, which is the specific incentive the litigation was about. The second term does related work: an agreement saying the agent will receive "whatever the seller offers" is not objectively ascertainable, because the amount cannot be determined from the agreement itself.
What NAR policy deliberately does not dictate. It does not prescribe the type of professional relationship, which may be agency, non-agency, subagency, transactional or customer, subject to state law. It does not prescribe the term, which its own guidance illustrates as possibly one day, one month, one house or one zip code. It does not prescribe the services. And it does not prescribe the compensation, which its guidance illustrates as, among other things, zero, a flat fee, a percentage, or an hourly rate. Those four blanks are the negotiable surface of the document, and the term and scope are as worth attending to as the number, because a long exclusive agreement over a wide area binds a buyer to one professional for every property in it.
Two relationship labels a buyer will meet and should not confuse with representation. Dual agency is a single agent or brokerage acting for both the buyer and the seller in the same transaction; it is permitted in some states and prohibited in others, and a written buyer agreement is still required where the participant is working with the buyer. Transaction brokerage is a non-agency arrangement in which the professional facilitates the deal without representing either party's interests against the other's. Both are creatures of state law, both are disclosed on forms prescribed by state law, and neither is covered further here.