Name three things that if a candidate does in an interview, then you should begin to question his overall professional caliber and that indicate that you are dealing with a less than strong candidate.

They make excuses - when people have to spend effort explaining why they said/didn’t say things, then that should raise definite questions in your mind.  Strong professionals don’t make excuses/say stupid things in business, so why should that happen in an interview?  They know how to focus on and make a point, and communicate their thoughts clearly.

They don’t give you straight answers to your straight questions - as a successful manager or businessman, you are providing straightforward, clear, and satisfactory answers to others all day long.  There’s no reason that this should not be the case in an interview as well.  People unable to do so are ones that you really have to question in terms of their caliber, intelligence, and/or integrity.

They can’t give you answers with any depth or detail – if a person has actually been involved or handled a situation or task first-hand, then they should be able to tell you how that thing was done to whatever level of detail that you ask.  The inability to do that is a reflection that someone is not nearly as familiar with or capable of doing something that they claim they are.

They can’t give you a good example, or are unable to explain why - for anything a person claims that he’s actually done or can do, he should be able to give you a good example of it or explain clearly how he does it.  People who do things well are able to do so because they know a process that works and are confident in.  They should be able to simply and clearly describe that process and/or achievement if they’re really any good at it.