In both cases, your opponents have points, up to a point.
You need some sort of justification for the claim, even if it is not personal authority. In particular, if you are actual talking about quantitative easing, that is something much more complex than literally printing money.
There's no actual point to saying that something isn't working, unless you have something better in mind. Consider the many people who believe that the whole of society is horribly broken.
Since your claims arent flawless, and their responses arent completely invalid, one thing you could do is pretend they made better versions.
OK, I do need to back that up. Well, most economists believe...
Ok, there is no point in just complaining. Maybe the government could put together a panel of experts to come up with alternatives.
Since your claims arent flawless,
What does that mean? I would expect no one's claims to be flawless, but even if OP claimed the sky is green, claiming that he is wrong because he's not a physicist is still wrong.
and their responses arent completely invalid
They seem pretty much like obvious examples of fallacies to me.
Your suggestions are possible ways to segue from what OP said into a better discussion, but the replies quoted or paraphrased above aren't conducive to such a discussion.
Especially in the comments of political articles or about economic issues I find myself arguing with people who question my authority about a topic rather than refute my arguments.
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Examples may be:
1:
Me: I think money printing by the Fed will cause inflation if they continue like this.
Random commenter: Are you an economist?
Me: I am not, but it's not relevant.
Random commenter: Ok, so you are clueless.
2:
Me: The current strategy to fight terror is not working because ISIS is growing.
Random commenter: What would you do to stop terrorism?
Me: I have an idea of what I would do, but it's not relevant because I'm not an expert, but do you think the current strategy is working?
Random commenter: So you don't know what you are talking about.
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It is not about my opinions above, or even if I am right or not, I would gladly change my opinion after a debate, but I think that I am being disqualified unfairly.
If I am right, how should I answer or continue these conversations?