As others have said, shitty is entirely subjective.
But pirated is a really easy problem to solve. Just run it through an identifier like Echoprint.
I strongly disagree that shitty is entirely subjective. Contextually, "shitty" could mean music recorded on a cell phone, or tracks that were 2 seconds long, or tracks that have been transcoded 7 times and sound like they're being played from a walkie-talkie at the bottom of a well.
I can understand why a music platform might want to enforce some standards of professionalism or technical competency, even if they didn't want to do so for matters of taste.