Everybody has their own ways of classifying and typifying people. In my case, my taxonomy would depend mostly on the subject at hand and somewhat on my mood. When it comes to responding to a given question or proposition or point of view, I find that people generally fit into two broad stereotypes (or a third narrow one) - those who have difficulty in clearly and openly agreeing (let's call them the natural nay-sayers), and those who have difficulty in clearly and openly disagreeing (the natural yea-sayers). The third category consists of those mature, evolved, unflinching individuals who agree with what they agree with and disagree with what they disagree with, and stay that way. (Sometimes I wish I could put myself in this class.) But since this is a very thin slice of humanity, and in any case a bunch of folks who don't seem to be plagued with issues such as doubt, uncertainty, paradox, etc., and who don't feel the heat of social or economic or political pressure, we would do well to leave them alone.
Natural nay-sayers tend to start their responses with a No, even when they agree with the given proposition. Quite often you'd find them shaking their heads in dissent even before you've finished saying your piece. And quite often, you'd find that in the final analysis, they're in agreement with you. I am constantly amused by the typical "No, I agree with you" response - the hallmark of this type. Some natural nay-sayers however are not honest enough to admit that they agree. They start with a No, which happens to be the typical nay-sayer's favourite word, and proceed to give you their opinion which, it turns out, is more or less the same; but they will not accept that it is essentially similar to (or at least somewhat aligned with) what you just said (or at least some parts of it). In some cases, it may be the overwhelming persuasiveness of your argument that renders them unable to articulate that one vital thought that could establish their position of difference. So they know they disagree but can't cleary say where or why. But in most cases, I suspect, it is more likely to be a reluctance to accept something as given - even if they agree with parts of it - unless it is regurgitated and cast in their own unique style of expression (by which time it has become a different proposition). An extreme reaction of this sub-type is to say exactly what you said, completely ignoring the fact that you said it first, and pretend that you never did or they never heard it. So it's their idea now and they own the IPR on it. On the whole, the good thing about people of this type is that they leave you with little ambiguity - you more or less know what to expect: they've already voiced their disagreement and as your dialogue with them progresses, things can only get better.
Natural yea-sayers are, by far, more complex creatures, and in dealing with them things may not turn out the way you'd expect, going by their intial reaction. Their first response is to agree (usually they are nodding their heads in assent right through, while you talk) regardless of what they really feel or think. There could be numerous reasons (and, accordingly, sub-types) behind such immediate affirmation. There's of course the typical Sycophant. And the typical Diplomat. There's also the typical Eternal Optimist who'd agree with anyone and anything purely out of a feeling of bonhomie and good cheer towards all of mankind. Then there're those who secretly disagree but generally tend to shy away from confrontation, those who get easily swayed by forceful rhetoric and/or the loudest voice and/or the most powerful presence around, and those who don't have a mind of their own to begin with.
There are several ways of saying No, including the one that starts with a Yes. Some years ago I had a T shirt that said "What part of NO don't you understand?" and I used to think about that sometimes. I guess I have my answer now ... it's the part that is actually a YES. Someone needs to spell it out, if it has to be understood. Over the years, I have come to the conclusion that the best way is to look for areas of agreement first - start with an up-front Yes (if you like, qualify it with relevant conditions and provisions), before opening out the areas of difference. And even there, in that, seek resolution by way of a win for both sides. Peaceful dialogue, focus on real issues and common goals is by far the best way forward. Some people call this looking for the silver lining. We need this now, very badly.