What is an example of a violation of the Sherman Antitrust Act's section against group boycotting?

The correct choice illustrates a clear violation of the Sherman Antitrust Act, particularly concerning group boycotting. The Act prohibits actions that restrain trade and commerce, and when multiple brokerages collectively refuse to work with a discount brokerage, they are engaged in a coordinated effort that undermines competition. This behavior can prevent the discount brokerage from fairly competing in the marketplace, effectively isolating it from potential business opportunities due to the consensus among the other brokerages.

In this context, group boycotting occurs when businesses collude, influencing market conditions to stifle competition. Such actions can lead to reduced choices and increased costs for consumers, making it a serious infringement under antitrust laws.

The other scenarios do not align with the concept of group boycotting as defined by antitrust laws. For example, two agents agreeing to charge the same commission may suggest collusion, but it doesn't involve a concerted action to exclude or harm a specific competitor in the market. Similarly, an agent choosing not to represent a high-risk client is a personal business decision that does not reflect collective agreement among multiple parties to restrict trade. Creating an exclusive MLS could also raise competitive concerns, but unless it's part of a group effort to exclude others intentionally, it doesn't fit the specific violation