They are asking for a situation where you've had to interact with a customer and what was your best response to a customer's question or need.
I would give you an example, but this needs to be your example, not mine. I'm guessing this is either for a test or for a job interview, so you need to think of how you've provided a customer with the best service. They need to know how far you would go to ensure the customer will come back to your business. Good luck.