Disagreeing with well-intentioned experts

Here's a bit of a random idea but that it's interesting to explore, not sure how, but I'd like to find an answer to this question.

How can I frame my disagreement with someone that knows more about the subject matter than I do?

Say, a keynesian economist, well.. that's a bad example, because I understand, or I think I understand, the premise of their mental models and I think it's total bullshit.

But say someone like the economist from the book Princes of the Yen, who talks about the wonders of Quantitative Easing and understands the risks of QE programs but sees that a well-run QE program can be benefitial in the short and long term.

This idea feels and rings incorrect to me. But this guy clearly knows multiple orders of magnitude more than I do. So what's my standing to disagree with his idea, really? It's just intuition. Intuition that he's wrong, but I can't go down in the mud of the argument.

Well, actually, thinking about it, if I were talking to him, I could attempt to probe his arguments from the start and attempt to find the place of disagreement. Which of the premises he basis his argument on is where we fork-off.

So where is the disagreement? What's the root? Is it experiential? This guy is clearly a very bright guy, seems to be honestly curious and willing to take his conclusions wherever reasoning takes him (not sure if that's true, but,  let's assume it is for the sake of exploring this line of thinking.)

Is the disagreement based on our lived experiences? At some point, regardless of the fact that we could both be following reason, we could find ourselves in completely opposed conclusions under the same set of facts.

Again. What's the source of the disagreement? What's the element that makes the logical conclusions under same facts diverge?

This is what I'm not sure of. This is the basis of the question.

UPDATE: After 

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