Where have you worked? How do you handle rush hour? How do you handle customer complaints? Ask the interviewee for examples of such situations. My first real job was as a waitress and one of the questions was if I could "make change". Nothing was electronic back then. I was hired because I could manually count back correct change to the customer. Nowadays everything is computer so no one needs to think about counting back change.
You can review the employer policies with the interviewee and ask if he/she foresees any problems.