If a listing agent represents a seller and an unrepresented buyer wants to view their listing.  That listing agent or an agent acting on the listing agent’s behalf may show the property without a “Buyer’s Agreement”  Reference Site: https://www.nar.realtor/the-facts/nar-settlement-faqs  Article 61

If the MLS Participant is working only as an agent or subagent of the seller, then the Participant is not “working with the buyer.” In that scenario, an agreement is not required because the participant is performing work for the seller and not the buyer.

Other situations include Open Houses, Rental Showings initiated by a property management company/landlord, and various tasks like property reports and opening the doors for inspectors and appraisers. Non-NAR affiliated real estate agents in states where Buyer Agreements are not required would also not be required to have a Buyer Agreement.