As a practical matter, how do you detect this kind of "evasiveness", and differentiate it from (say) plain old introversion or nervousness?
Suppose you're having a conversation with someone and in 15 minutes one of you chosen at random is going to have to trust the other with his/her life. What kinds of signals indicate that the person is trustworthy, understands the potential future, and is accurately representing him/herself?
There are some people where I never feel the kind of connection I'd want to feel in that scenario, and others where I feel it fairly early on in the interaction. Just a kind of straightforwardness, not extraversion or social comfort.
That is certainly a risk with any notion of "culture fit", but any time someone who cares about culture is interviewing someone that fit is being evaluated to some extent.
In other words, is the candidate someone who has a rational meta-process going on about his/her decisions and is able to refine his/her approach based on learnings. I'm ideally looking for small things that show clear evidence of that kind of thought process.
As for body language, I agree, and I think my choice of the term "poker face" was a bad way of describing a certain kind of evasiveness which can indicate bad motives or bad people skills, either of which can make the person a bad hire.