It depends on the field of expertise.

Some fields are such that they are hard to be expert in, but it’s trivially easy to verify expertise when observed. For example, playing tennis. It’s easy to identify a good tennis player even if you can’t play tennis at all. Another classic example is cooking. Even the most caveman-like philistine knows good food.

On the other hand, for some fields, verifying expertise (or ‘mastery’) is as hard as achieving it. Academic disciplines — particularly technical ones like science — are examples. In those cases, you probably have to rely on a trusted authority to verify legitimacy. Without that, you can’t distinguish the accomplished experts from the crackpot blowhards.

I don't think it's as easy as you make it sound. I probably couldn't differentiate an expert Shandong chef from a generically skilled chinese chef, even if I like their cooking. It's difficult as a non-expert to even know what the differences are, let alone be able to see (or taste) them.

> For example, playing tennis. It’s easy to identify a good tennis player even if you can’t play tennis at all.

I'm not so sure. Identifying good talent is difficult when it comes to sports. There's an entire industry of scouts that try to find decent players ahead of the others. More so, they are tasked with finding out why a particular players is good. It's anything but trivial.

I’m just demonstrating that the two categories are different, which they clearly are.

Not that one is trivial and the other is impossible. Of course, if you want to do any task well it becomes nontrivial.

It could be both at the same time.

One can be a master in certain art, yet can't explain what's going on.

Think cooking: Many chef "searing steaks" to "keep juice in". It don't keep juice in, but it taste good.

Think language: Most native speaker can form grammatically correct sentence, but they can't really explain how. Yet many linguists, knowing how some languages work, keep bullshitting about another language.

> Academic disciplines — particularly technical ones like science — are examples

Technical sciences are much easier than the social sciences. Social science is much more full of people who have no clue what they are doing than technical sciences, because technical sciences can be verified by experiments while social science is mostly about trust.

There's an entirely legitimate question here behind this quip.

I don't think there's a magical answer, but one approach I've found is to try to be a mini expert in a tiny, tiny slice of a bigger area (usually bridging over knowledge from some adjacent area I know). This means that I can then evaluate those who talk about this tiny area, and get a good baysian guess as to there broader expertise from there.

Typically someone who has spent their life working/researching/teaching in that sliver of a domain. It is also important to remember that experts start losing their expertise once they have retired or no longer actively working in that domain.

So you are looking for someone with many years of work experience in being an IC or lead or CEO or a researcher with a lab or PhD in that domain with lots of papers in highly respected/ranked conferences/journals. In domains you have no idea about, you might need to first read a book or general article which links back to such experts/sources and then it is easy to find the cluster of those experts in that domain.

This sounds like the appeal to authority fallacy.

My first test is to ask the expert to explain a complicated concept in their field, which I know a little bit about, in plain language that anyone can understand. Asking a few follow-up questions can usually separate the true experts from the fakes.

This is true! A general journalist who has studied up a domain and written an article within a week cannot stand up to this kind of deep questioning.