Keep Lemmy small. Make the influence of conversation here uninteresting.
That’s a significant constraint and it’s probably possible to reuse a lot of the costs in developing a both for another platform.
Or … bite the bullet and carry out one-time id checks via a $1 charge.
Yeah, making identities expensive helps. But…you note that the bot that OP posted clearly had the bot operator pay for a blue checkmark there. So it wasn’t enough in that case.