Have you had any transactional training on how to handle the various types of customer personalities?
There are many techniques for handling various types of customers and the interviewer would like to know if you've had any of that training or experience. Expect questions about what you've learned both on the job and off, both in structured learning environments and what you've basically picked up or embraced on your own. If you've had customer training now is the time to bring that out, but if you haven't you should at least be prepared with some examples for handing different customer types. Being confident and able to convey that you know what you're doing allows the interviewer to picture you at their company in the position performing as a customer service representative. Be clear, be thorough and keep building your case.