Great question - this is indeed an issue as it's difficult to prove to others that you are/aren't doing something which they cannot verify without gaining full access to all of your servers in their entirety.

However, our trust comes from the many years that we have operated this business in this fashion and the good faith of our users.

With that said, we have been in discussions with some well known privacy organizations regarding the setup of an auditing body that could verify these sort of things.