It never ceases to amaze me that people continue confusing "agency" and "compensation".
The key concepts of procuring cause are referenced in this definition from Black’s Law Dictionary, Fifth Edition (and quoted from NAR):
“The proximate cause; the cause originating a series of events which, without break in their continuity, result in the accomplishment of the prime object”
This is a direct quote from NAR's code of ethics. NAR also provides Test question and test cases showing how to get paid vs agency.
First, I'd reccomend reading my blog,
http://realtyworldwichita.com/blog1/index.php Then, check Realtor.org on procuring cause. And then check reality. The buyer can ask the relative not to participate, and ask another agent to write. The Relative agent does have a claim to the commision, but to collect, they would probably have to ask a board of peers from the local MLS to get it. If I were the agent who was asked to write the offer, I would ask the buyer to sign paper stating they didn't want Relative to be involved, and then give the Relative agent and the seller's agent a courtesy call to share info. I would also tell buyer what I was going to do, and ask them to contact Relative agent and share the same.