The only thing I ever found useful interviewing people - and it always seems to have worked out well - was asking about real work related situations. What would you do/have you done in such and such situation?
i.e. do they have the skills, theoretical knowledge and sense of professional boundaries* to make the right choices.
*Knowing when to ask for advice and not just persevere is often as important as knowing what to do. I wanted people who know when to stop digging.