Here is the biggest credibility problem: hearing adapts. You can't judge accuracy of a reproduction system unless your hearing is well acclimated by daily listening to the absolute standard: physically generated music, with no mics, wires and speakers in the room, just musicians using their fingers and lips to make sound.
One of my audio gurus, Siegfried Linkwitz, gave a talk at the AES convention a few years back which castigated audio engineers for NEVER listening to live music. The people who judge tests like CD vs. SACD listen to speakers all day, every day of their professional life and NEVER go to acoustic concerts. Even if they spend a few minutes in the studio listening to real music being played, the setups are typically one to three musicians at a time, or musicians in separate rooms, and all studio rooms are carefully deadened to increase separation!
This means that AUDIO ENGINEERS ARE DEAF TO THE SUBTLETIES OF MUSIC PLAYED IN A ROOM. They were raised listening to speakers and never learned what real music sound like.
I found this to be an excellent comment, one that helps explain why some listeners find it easier than others to distinguish different levels of reproduction. The best listeners I know of are also those that often go to live music concerts. And I don't go enough myself. Our memories of the real thing fade and adjust over time.
Not only is it imperative to expose yourself to live music as often as possible, but there are other benefits as well. Attending live music events supports musicians, gets you out of the house, and is just downright enjoyable.
I plan on doing more. You?
