Sounds vaguely like my job as a Station Grade A up in Scotland. Generally it will be things about your competency and personality -
Talk about a time you dealt with a complaint / awkward customers/ intoxicated
Talk about a time you had to think on your feet
An emergency situation
Foreign/ Disabled Customers in a station.
A time you went the extra mile for a customer
Attitudes towards safety, customer care, customer satisfaction
A time when you worked together/ how you work in a team/ can you work alone/
A time you followed procedures/ can you follow procedures
Ive worked in Stations after being a Ticket Examiner. It's a bit of an eye opener working in Stations, some customer's attitudes towards you and your employer can be questionable you an be called all sorts and hear all kinds of language, you will deal with all sorts of people some nice and some very awkward, you need to expect the unexpected like during a service disruption and it all falls to pieces. You have to always remember your safety comes first when it comes to conflict situations and be able to avoid or talk your way out of them. I love the camaraderie with my colleagues, teams and traincrews, reuniting people with their lost property, getting people to their destinations, saving them a few quid with tickets and knowing you have done your bit. It has its hard days, but like everything in the railway- if you keep your head down, do your job, stay out of trouble- it's a safe, secure and well paid job. All the best in your interview.