The placebo effect is definitely a thing and it most definitely applies to a lot of the decision making applied to high end audio.Every perception is constituted by the brain with habit and bias, with an history, with fear and hope, then placebo is creative part of any perception...
But those who oppose placebo effect to explain any audible experience in audio remind me of those who explain walking by the different types of shoes, sandals,boots..... Hearing is not placebo mainly, and walking is not shoes mainly ...
But nobody walk the same in big boot and loose sandal....
Nobody hear the same looking at a 100000 bucks system and before a 1000 bucks one... Same Ears not the same hearing.... Same feet but not the same walking... placebo and look and style count for much in the 2 cases.... 😊😁
Then opposing placebo against any audible experience is not even wrong.... Most of the times it is simply beside the point...
It is only a weapon for the children in the "skeptic scientism boy club" to use against audiophiles....it explain nothing most of the times save very small borderline audible difference....
You cannot create a top audio experience or experiment with placebo effect ONLY.....Save if you use market hypnosis method for sure but it is another story.... I never bought upgrade anyway.... I prefer homemade embeddings controls....
My best to you....