Homework to be done before the interview:
It is essential to understand what we expect from this role. Facilitating events and making Scrum work is not the best description, as you can imagine.
What we, ourselves, know about Scrum? What do we want to achieve through it?
How are we going to evaluate the Scrum Master's work?
What is the level of our agility?
Based on that, the best way to interview a Scrum Master is to:
Put stress on questions that would give you a clear picture of how Agile the person himself is.
Concentrate on communication skills, personality type, and cultural fit rather than how to organize this or that event.
Give assessments based on real-life example situations. How would this person act? What would do to improve the situation?
Remember: Scrum Master should be the person, the whole team trusts and listens to. This person should be ready for challenges, for changes, and continuous improvement on the personal level first of all.