I've been seeing comments on HN praising how Apple respects users' privacy etc. Though I have a genuine question: how can we be so confident that Apple follows their claims while their software remain closed-source?

For client-side Google software like Android/Chromium at least we got to fork and remove the evil bits; we have built thriving communities based on that and everyone's got an alternative to Google. In the case of iOS/Safari do we trust Apple-provided binaries solely based on claimed policy / reputation?