> The buyer would know that maybe the seller still has the key, since cannot be rotated
If the buyer is a spammer, they won't care that the seller can still send non-spammy messages with the account. If the seller is a squatter/speculator, they have nothing to gain from interfering with their customer's account.
> A group of people cooperating can pretend to be 99999 people?
It would be easy to determine from the (anonymous) social graph that those 99999 people are only connected to each other and a small group of other (real) people. An algorithm looking at this graph could then select 100 people out of the 99999 group and require them to meet with 2 other distantly-connected people at a specified public place. If less than 102 people show up, then those 100 lose trust points. That's how I guess it would work, anyway.
What if the seller is a spammer or scammer, and first sells the account, remembers the private key, and a bit later starts spamming or scamming
> It would be easy to determine from the (anonymous) social graph that those 99999 people are only connected to each other and a small group of other (real) people
If the "group of people" is small, yes. I didn't say that the group was small though.
If it is larger, and they arrange the connections in realistic looking ways (for detection algorithms), then they can get away with it. Think of an island where most people are connected with others on the island only -- and maybe 10% of them connected to people on the mainland. Something like that can happen in real life I suppose, and the "group of people" (possibly many, paid by a company or a state) could construct such graphs and pretend to be more than what they are
> An algorithm looking at this graph could then select 100 people out of the 99999 group and require them to meet with 2 other distantly-connected people at a specified public place
That's an interesting way to try to handle that. However, first the algorithm would need to realize that a part of the graph is suspicious. (And people would need to be really motivated to, in real life, actually go to somewhere :-) ? what of they're busy with friends and family)
If the buyer is a spammer, they won't care that the seller can still send non-spammy messages with the account. If the seller is a squatter/speculator, they have nothing to gain from interfering with their customer's account.
> A group of people cooperating can pretend to be 99999 people?
It would be easy to determine from the (anonymous) social graph that those 99999 people are only connected to each other and a small group of other (real) people. An algorithm looking at this graph could then select 100 people out of the 99999 group and require them to meet with 2 other distantly-connected people at a specified public place. If less than 102 people show up, then those 100 lose trust points. That's how I guess it would work, anyway.