> You should start making and selling espresso machines then, since you know more than coffee professionals about them.

That doesn't really follow. If I think five-figure coffee makers that perform a rather simple mechanical function are overpriced, I should start selling them myself?

> Same with high-end audio gear.

I'm talking about equipment whose qualities cannot be measured nor perceived in a double-blind study. Pure make-belief:

"Audiophile publications frequently describe differences in quality which are not detected by standard audio system measurements and double blind testing, claiming that they perceive differences in audio quality which cannot be measured by current instrumentation,[26] and cannot be detected by listeners if listening conditions are controlled,[27] but without providing an explanation for those claims."

https://en.wikipedia.org/wiki/Audiophile#Controversies

> Do you also go to museums and say "I could have done that" to every painting?

No, I've got better things to do. Having said that, modern art certainly is rife with pretense.

I think you are overlooking one important aspect with espresso machines. You can get much less expensive machine that will create same tasting cup. But only if you do few cups a day not few hundreds. They are expensive because they are heavy duty, they perform and you dont have to clean them as much because they are made with much higher precision and they last longer. This is highly valuable - you dont want you main source of income to die on you in middle of the day.

In the long run price difference is well worth it.