Joel On Interviewing 13: The Challenge
This is fun. Throughout the interview, you look for the candidate to say something that is absolutely, positively, unarguably correct. Then you say, "wait a minute, wait a minute," and spend about 2 minutes playing devil's advocate. Argue with her when you are sure she is right.
Weak candidates will give in. No Hire. Strong candidates will find a way to persuade you. They will have a whole laundry list of Dale Carnegie techniques to win you over. "Perhaps I'm misunderstanding you," they will say. But they will stand their ground. Hire.
Admittedly, in an interview situation, you are not equal parties. Thus there is a risk that the candidate will be afraid to argue with you because you are in a position of power over him. BUT, good candidates will tend to get fairly passionate about the argument, and they may momentarily forget that they are in an interview, and they will get very involved in trying to convince you. These are the people we want to hire.