Pop quiz - Would you accept a placebo if it improved the sound
Now you're walking on thin ice! Some psychologists posit the placebo effect is just a creation of our mind while other state that the effects are real, insomuch as the subject can really feel them. Now it depends on which camp you're in, and since psychology is far from being my strong point I won't try to take the quiz.
However I will state that while offering free tweaks based on the placebo effect is just fine, while charging good money for them is a scam!
Now you may ask me why, as part of the placebo effect is "the more it costs, the better it works"? Well, just because (1) this diverts funds from buying tweaks that really work, and (2) because the gullible buyer might have his beliefs overturned anytime, and just be left with less money and a smart looking "thingy" of no use. Well, it might not be a fraud - legally speaking - but I find it to be highly immoral!