The interviewer would like to know that you remain professional, helpful, and calm when dealing with customers of all kinds. If you can, give a specific example of a time when you successfully assisted a challenging customer.
"As a Telecommunications Specialist, I'm often called out to assist customers who are frustrated, disappointed or angry due to equipment failure. In these situations, I always listen first, then validate the customer's feelings before jumping to solutions. Technical disruptions can be frustrating, and I want them to know I am on their side. Once the customer feels heard, I then begin troubleshooting the issue and working to resolve it. I won't leave a service call until I know the customer is delighted."
"Challenging customers are present in any industry, and I have experienced a wide range of them in my career, so far. I find that upset customers just feel like their problems are not heard. By offering an empathetic ear to their situation, I can usually diffuse the situation immediately. I will ask them what they feel a suitable solution is and then provide that solution, or as close to it as possible."