The interviewer wants to hear that customers are your priority. Tell the interviewer that you would graciously stop what you were doing and start by genuinely listening to the customer. Next, share that you would apologize to the customer and take whatever corrective action was necessary. Be sure to mention that most challenging customers do not take much time, and they just want to know that their opinion is being heard. Finally, be sure to say that once you have the customer on their way, you would go back to working on your task.
"I have extensive training in customer dispute management. If a customer is ever unhappy with their service or product, I would be sure to apologize and ask them how I can ensure they become a satisfied customer again. Most customers will tell you exactly what they want, to satiate their needs."