You don't need to identify who is an expert and who is not by yourself: experts (scientists) compete with and cross validate each-other. I.e. experts themselves will self-select who qualifies as experts. And since there are a lot of them and there is also a pretty strong competition it's pretty unreasonable to say that there is somehow a large conspiracy because it should have to involve basically everyone.
And not just in one field! E.g. sometimes climate change denialists say that climate science is not even real science and that these people are just self proclaimed scientists. But the thing is that all fields of sciences (at least all natural sciences, engineering and mathematics) are interrelated. All of these have boundaries touching each other and all fields will have at least some scientists working on these boundaries with people from another field. So no field can simply fake it. In other words, basically everyone who has published in the past few decades will have a finite Erdos number :).
Also, not only you can trust the experts, but you don't really have any other sane/viable choice.
> I've seen this play out in companies; businessmen in positions to promote technical people, often making some very poor decisions.
This is true. What I say to people (small business owners or startup founders) is that you can't pick a co-founder, a tech lead or even a good subcontractor without having the technical knowledge yourself.
But that's pretty a different issue. First of all, here you need to pick a specific person for a specific role where you'll then have (want) to trust all (most) of their decisions and you don't have anyone to compare these to. Also, it's many decisions based on a small amount of data.
While what we are talking about is listening to experts who mostly say the same thing (the scientific consensus) and it's a very few decisions based on a huge amount of data (research, experiments). There are, of course, times when the consensus has not settled, when experts won't agree, but then you know that they don't know enough yet.
Which is pretty rare and the reason you know they are wrong is because science proves them wrong - later. The thing most people don't get is that if you want a pick viable strategy, then it's not enough to simply criticize one of the candidates (candidate strategies), in this case the "listen to science/experts". You have to evaluate the alternatives too. Because you have to chose something, because you will pick and follow one strategy.
I've already suggested a lot of people to come up with an alternative but I'm yet to see one. Of course, you'd have to explain why it works better.
They aren't wrong because the science proves them wrong, though- they're wrong because they happen to not be right.
Sometimes, the scientific or quasi-scientific institutions we have just aren't sufficiently uncentivised to align themselves with the truth! Modern Researchers are beholden to grantwriters, and grantwriters are biased in what sort of peojects they'll give money to. Specifically, low prestige problems are underfunded.
An example I heard about was light-boxes for SAD. There were some studies with a few lights that helped a bit; nobody had done studies with a ridiculous number of lights to see if it solved the problem completely; one guy did, and it fixed his wife's SAD. In absence of data, anecdata rules.
Alternatively, entire fields can be compromised when they're politicised. The soviet union's physics was good- the scientific method worked there, and if you wanted your ideas about physics to match up with reality, you could do a lot worse than copying the most popular soviet physics world-model! Just don't do it for biology, or genetics, or sociology. (Actually, you probably shouldn't trust western sociology, either.)
One person shouldn't be able to outperform the scientific institutions of the world, but it can happen when they're unhealthy.
I've seen this play out in companies; businessmen in positions to promote technical people, often making some very poor decisions.