They can print ecash without sats backing the mint so yes need to trust the mint.
Please self-host your mint for best practices
Discussion
self host so we can get in on the printing action ourselves. like the way you think! 🤑
in all seriousness though, so we operate under the assumption that they are being sneaky and there is little we can do about auditabilty so use them for small private transactions but dont rely on them for much more