......Those CLAIMING they can hear differences must do so under controlled and blind conditions that these differences exist without a shadow of a doubt.......
Isn't the burden of delivering proof up to the one making claims ?
Yes.
Blind testing is, as Ethan points out, the "Gold Standard' of proof in all other areas of science.
Blind tests allow you to change just 1 factor in the chain (in this case the device that is being tested) and eliminate other factors that could impact the results (in this case the knowledge of what is being tested...along with preconceptions, and expectations of the listener).
How could it be that in all of science, it is only in audio that blind tests are not valid? If unknown factors exist that impact audio perception...blind tests would reveal that. They do not.
Delivering scientific proof is especially required of those who not only make claims...but profit from them.
The PSAudio Accessories page includes Audiophile AC power receptacles ($50-$400), AC power cables ($129 to...well if you have to ask), and Noise Harvesters ($99-$400). Any impact these devices have on the final results (the amplifier's or speakers output) could easily be measured, or perceptually tested in statistically valid blind tests. None have been.