In fact, this depends on interviewer. Most interviewers have been in this role for years if not for decades and they may be interested in different things.
As for me, I usually start with general questions: who are you? what do you do in life? Then: How did you learn about Servas? Why are you interested to join us? I also speak about Servas myself and observe the reactions of the person.
I never had to refuse anyone. A few times, I had a feeling that this person was not someone we needed. In this case, I simply discouraged the person from joining. It is not that difficult.
Today, there are too many different hospitality exchange organisations, and you can join most of them without this interview hassle.