A long, long time ago (no, not in a galaxy far, far away - but it was Southern California, so it may seem like another galaxy), a friend of mine participated in a review of some "incredibly innovative audio equipment that sets new highs in hi-fidelity" or some such jargon. I'm not sure when all this took place, but I met him in the mid 70's when he owned a small recording studio so it had to be before that. He had already been a musician, music producer, and was involved in the recording industry for years.
In any case, the organizers of the event had access to Hollywood Bowl for an afternoon, and set up a demonstration of the equipment for 25 or 30 local studio engineers, musicians, audio enthusiasts, hi-fi reviewers, etc. The type of equipment was not revealed and was set up behind a large curtain. The participants were told the music was previously unheard live rehearsals, and were encouraged to write down all impressions and observations - both pro and con.
Unfortunately, the "incredibly innovative audio equipment" was not very well received. The cons far outweighed the pros: "lifeless and flat", "overly exaggerated high freq.", "sounds like a low-end stereo". Some of the kinder reviewers thought it might sound better inside a room instead of outdoors - "You can't expect any equipment to perform well under these conditions".
Anyway, to make a long story short, after gathering up the reviews of the equipment, the organizers dropped the curtain to reveal a live orchestra.
At least two of the reviewers had guessed what was going on because it was written on their notes, but most were quite surprised.
I'm told this type of thing has happened a few times, but this was the only one I heard specifics about.