Add "Referral Partner" Field in Contact Details
Have a field for: Referral? "yes" or "no"
If yes, another field opens up to have the Referring agent's contact information entered so it links to the client, and another field for either $ or %. If there's no referral fee involved, someone can just put 0 (zero). Once an opportunity is created, that information would populate, and the agent could click a toggle to push it to the DA.
This would help keep track of referrals easier so they wouldn't have a chance to get overlooked and missed. This would also be a great way to track where referrals are coming from and where they are going.

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LABS Team commented
Please either add Referral Agent to the Relationship drop down OR better yet add a new field for Referral Agent to associate a contact for an agent with a client.
The issue with making the Referral Agent in Relationship would of course be confusion about if they are related to the client etc.
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LABS Team commented
When a new referral agent is added to your network, that agent should be added to database Contacts for easy communication. This should be done with an "import contact" button, either in the individual's dropdown info or to add the network as a whole.