Can't, except as you note. Best trade your fiat for something actually auditable through cryptographic means ASAP. :) (for a less quippy answer: they could sho

Can't, except as you note. Best trade your fiat for something actually auditable through cryptographic means ASAP. :) (for a less quippy answer: they could show their fiat liabilities through these means and have a third party bank attest to their fiat account assets (or an encryption of their fiat assets). At least then you'd be trusting some established bank and not just some sketchy cryptocurrency industry company)