Which of the following is an antitrust violation related to collusion?

Agreeing on commission rates with other brokers constitutes an antitrust violation related to collusion because it undermines free market competition. Collusion among brokers to set commission rates can lead to price fixing, which is illegal under antitrust laws. This practice distorts the natural pricing mechanisms within the real estate market, ultimately harming consumers by limiting their options and potentially raising the costs of real estate services.

In contrast, discussing common marketing strategies may be permissible as long as it does not lead to price fixing or other anti-competitive behaviors. Offering discounts for exclusive listings could be seen as a competitive practice as it encourages brokers to attract clients through unique value propositions. Adjusting services for client retention focuses on customer service and does not directly impact pricing strategies across the industry. Hence, it does not rise to the level of an antitrust violation.