Final answer:
The seller is considered the third party to a buyer representation agreement, which is a contract made between the real estate agent and the buyer.
Step-by-step explanation:
When Sam enters into a buyer representation agreement, the agreement is made between Sam, acting as the real estate agent or broker, and the buyer. In this context, a third party refers to an individual or party that is not directly involved in this legal contract. So, of the options provided, A The seller would be considered the third party to the agreement since the seller is not a signatory to the buyer representation agreement, which is a contract between the buyer and the buyer's agent. The buyer and Sam are the primary parties to the contract.