What are we distinguishing experts from? People who claim to be experts, and even think that they are experts, but are not. Having been around a bit, I find that in most cases such people have a distinctive cognitive style which can itself be detected in various ways.

Real experts make an attempt to explain things properly - they may simplify, but the simplified argument always maps onto a proper argument that has the same effect. Non-expert experts tend to explain mysterious points in ways that you still don't understand, or in terms of explanations that seem to make sense at first, but turn out not to contain everything you actually need to understand what's going on.

Experts of all kinds tend to have some expertise on a wide variety of things, and in some of these you will also know something and can check whether they really understand or not. Non-expert experts may claim to have wide knowledge, but tend to be very specialised. They tend to mess up in the areas that you can check.

Non-expert experts tend to make detailed and lengthy calculations based on shaky presumptions. Expert experts can calculate, but won't bother you with it - they will instead look at the same thing from several points of view - each viewpoint chosen to illustrate to you what's really going on.

Non-expert experts can draw some really bizarre conclusions - and won't really notice that they are bizarre. Expert experts will notice when one of their own conclusions is bizarre, and will tell you of its oddness. And won't draw quite so many such conclusions in the first place.

There are usually things you can check. Have they used the correct units? Experts won't confuse watts with joules, or force with power. They won't talk as if volts or amps are powerful. They won't say that 40C is twice as hot as 20C.

Non-expert experts tend to have particularly strong views about the morality of people who disagree with them, and regard that as important to understanding the subject. Expert experts may have strong views about the morality of the non-experts, but generally don't talk about it as they regard them as irrelevant to understanding the subject.

Non-expert experts tend to try and make themselves look smart. Expert experts tend to make their listeners feel smart.

Go read something by Richard Feynman, or something like "The selfish gene". Or the sequences. Once you get used to what a proper explanation is, it's much easier to avoid being fobbed off with something else.

Back to the caveats. First, no deliberation makes practice useless. Having spent approximately 8 hours every day sleeping for the past 61 years (178,120 hours) hasn’t made me an expert on sleep. Likewise, deliberative but ineffective practice methods deny us top-level expertise. Early studies of Morse Code experts demonstrated that mere deliberative practice did not guarantee best performance results; specific training regimes were required instead. Autodidacts with insight and aspirations to attain the highest performative levels in their domains eventually realise how important getting the “right” coaching or teaching is.