Thank you for your question.
It sounds like you did not have a written broker agreement with the Buyer. In which case, the buyer may be able to terminate your services at any time and argue that you are not entitled to a fee. By California, you may need to prove "procuring cause" of the ready, willing and able buyer.
Commission disputes boil down to what is referred to in the industry as "procuring cause." The agent who ultimately caused the buyer to purchase the home and earned the commission is the procuring cause agent. That procuring cause agent might not be the agent who obtained the offer from the buyer, presented the offer and successfully negotiated the seller's acceptance of that offer.
Now you have draft escrow instructions showing your name as the buyer's agent, if the buyer had a change of heart, feeling that you did not undertake your duties and were not the procuring cause agent, that would be an argument they could put forth to the court.
Your best argument is that your assistant introduced the buyer to the property and submitted the offer to purchase to the seller. Thereby arguing that you were the procuring cause and that you created an implied-agency agreement, so you are entitled to the commission.
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