Once you learn how you are fooled by expectation bias, its not that hard to compensate for it. No need for time consuming blind tests that typically can’t be done without help. For me, that means listening to a day or two and then switching back. Its not uncommon that I believe I hear improvement the first minutes or even an hour, but it won’t last unless its really there.
But people who don’t believe in improvements that others hear are usually the kind of people who refuse to believe there is improvements that they don’t understand. The fact that they don’t understand how an improvement can happen is inconceivable, and hence its not really an improvement at all but just bias from sighted listening.
I don’t understand gravity (very few people do), but I still hurt myself if I jump from the roof. 