Final answer:
Mediation is the most appropriate method for Rachel and Kourtney to resolve their dispute over the cooperative broker commission and preserve their working relationship.
Step-by-step explanation:
Mediation is the most appropriate method for Rachel and Kourtney to resolve their dispute over the cooperative broker commission and preserve their working relationship. Mediation is a process where a neutral third party helps facilitate a discussion between the two parties in order to reach a mutually satisfactory agreement. Unlike litigation or arbitration, which can be adversarial and result in a binding decision, mediation allows Rachel and Kourtney to maintain control over the outcome and work together to find a solution that satisfies both of them.