Really?? I want people working for me that are experts in their chosen field! Expert knowledge doesn't mean "I know everything", it means "I can tackle any problem given to me on this subject with the right timescale allowed". Working knowledge means they know how it works theoretically in a lot of cases. There is something a bit backwards about your approach to hiring people IMHO. But then, there are a million interview techniques and criteria so don't take my opinion in the way that makes you think that I think I know more about your business than you. If it works for you that's all that matters.