The interview process is more casual than other job interviews I've experienced. Try your best to be yourself, as the customer service is integral to the role. Being friendly, open, and easy-going will be very beneficial. They want to see how you interact with strangers - and how you can be cheery and good spirited even when under stress (in an interview). Be prepared to provide many examples of the customer service you've done. Always have an example of a time you've dealt with a difficult customer. We have a customer satisfaction model called the LATTE model at Starbucks - Listen (to their concern), Apologize (about the mistake or inconvenience), Take Action (make them what they ordered), Thank (thank them), and Ensure Satisfaction (if you make them the drink they wanted, make sure there aren't any issues with the re-made one). If you can weave those elements into your answer when asked about dealing with customer complaints, you'll be golden!