There is sufficient transparency to know violations are occurring, and we can usually rule out other actors circumstantially to give us a suspect – often Facebook, Google, or another "Big Tech" company. There isn't enough transparency to conclusively prove it's them (as opposed to some secret shadowy conspiracy who've concealed all other evidence of their existence – which we do need to rule out, for the innocent-until-proven-guilty standard), but that's what the legal fact-finding process is for.