Final answer:
The open buyer agency agreement provides the least protection for a buyer's broker, as the buyer can work with multiple brokers and is not obligated to purchase exclusively through one broker, risking the original broker's commission.
Step-by-step explanation:
Among the options, the open buyer agency agreement offers the least amount of protection to the buyer's broker. In an open buyer agency agreement, a buyer is free to work with multiple brokers and is not obligated to exclusively purchase through any one broker, which leads to the risk for the broker of not being compensated if the buyer purchases a property through someone else.
An exclusive right to purchase agreement ensures that the broker receives commission if the buyer purchases any property during the agreement period, providing a high level of protection. The exclusive agency agreement also offers protection but allows the buyer to purchase a property on their own without owing a commission to the broker. A net listing agreement is a term that typically applies to sellers and their brokers, not buyers and their brokers, and thus is not directly relevant in this context.