A bank is a serious and professional environment and every once in a while, a customer comes with an issue that is well beyond a Teller's ability to handle. For this question, your interviewer is looking to hear that you will handle these customers with the respect and ease necessary to ensure their satisfaction in service of the institution. Whether you'll be dealing with a customer that received poor service at some point or was dealt a mistake by the organization, your interviewer will be looking to hear that you have the ability to remain calm and treat customers with the respect that they deserve while making all attempts possible to solve their issue. In your answer, talk about your ability to use your communication skills to your advantage and how you use teamwork to solve problems at any level. Any real world example that you have would be good to talk about as well in your answer.