Collections are private. No other user can see your cards, purchase prices, sales history, or alerts. We don't have public profiles yet.
Future: you'll be able to opt-in to publish a "showcase" page with selected cards (for trading / selling), but this isn't built today and won't be enabled without explicit consent.
Our analytics aggregate anonymously — we know how many users own a Charizard Base PSA 10 but never which specific users. Your specific holdings are not visible to anyone except you and our support team (if you grant access for troubleshooting).