They generally don't expect you to understand how the credit card processing industry or payments systems network works. They know that its not everyday knowledge for people. They just want to make sure you are good at establishing relationships and can communicate effectively. This position requires you to be analytical and relational, so the questions will revolve around solving problems, dealing with different personalities, and whether you are comfortable interacting with people who are not in their best mood. Can you turn a conversation around from being negative to positive? Give an example of how you repaired a relationship with a customer or client.