Who was the procuring cause of the sale?
NAR has created a procuring cause/arbitration worksheet for use by local association hearing panels when identifying relevant issues and facts in determining questions of entitlement to "disputed funds".
If you are a member of NAR you can log in and see the worksheet here: Worksheet from NAR
The problem with 'procuring cause isn't it's existence. It is the willful failure of the industry to disclose it to the home buying public that is the problem. It is a problem because home buyers often fall into the trap of believing they can have any agent represent them beginning at any stage in the process.
By walking into a house with an agent from the company that listed a house they are likely going to be prevented from having representation of their own choosing. As Tom Wemett put it: "One date - You're married."