Home sellers will have better representation when they ask better questions BEFORE they hire an agent. An example of a problem the agent solved, and how they solved it will tell you if the person you're interviewing is a problem solver. Asking how they set their commission rate opens the door to a sincere conversation about agreeing to a rate that works for you.
Elon Musk asks applicants to tell him about the problems they encountered and how they solved them. From this question, you can tell if the agent was a key player in the solution or just a bystander. Ask for an explanation of how the firm or the agent set their commission rate in addition to asking about the rate. The answer to this question will give you an idea of where you fit into the calculation.