Correct, with all single signer ownership you can never be sure how many custodians there are

So you’re right and we would never be able to prove that any amount has changed hands or not, only assume that others wouldn't take the risk

Prove no, but it is not very likely IMO.

Sure, it is a network based on trust. But the whole idea of bitcoin's principle of trust is that you trust the majority of an entire community.

By making a deal with a single party for their wallet credentials you have to trust only the seller. One single party. In a shady deal involving a fortune.

And like I said, who would spend obviously phenomenal amounts on something and then never even touch it? When the buyer could simply move that trust from one party to the community simply by transferring the balance to a new wallet.

Of course the ripples in bitcoin's value would be unprecedented. But the buyer would hold so much of it that one way or another they would be extremely rich.

I'm not really talking about the sharing of keys in general by the way. Just about the thought of Satoshi's genesis wallet keys being sold this way.

I think what they were trying to say was that buying them off chain would be extremely unfavorable as the buyer gains zero of the protections that a blockchain claims to offer in this case.

And my original post wrote that bitcoin works in trusted environments, and maybe they didn't know that meant small networks of humans trusting each other with private keys off of the blockchain even though that was the only context possible, now they know so we’re just intentionally talking past each other at this point