I would ask how they maintain their credentials, what kind of CEUs do they do?
Ask how they interrect with physicians, give some examples of physician queries that went well and some that didn't.
I always like to ask "What is your favorite part of your current job?" "What is your least favorite?" This can give you some idea of personality and can lead into questions about strengths and weaknesses.
Does anyone have some standard questions they ask when interviewing coders? If so would you like to please share?