It doesn't have a global solution and it doesn't need to be implemented only on a specific technology-based system.
I mean, at Communick I offer Matrix, Mastodon, Funkwhale and Lemmy accounts only for paying customers. As such, I have implemented payments via Stripe for convenience, but that didn't stop from getting customers who wanted to pay directly via crypto, SEPA and even cash. It also didn't stop me from bypassing the whole system and giving my friends and family an account directly.
Right, so the gap I'm seeing is that anyone who wants to identity farm just does what you've done. The problem isn't the assurance that you receive, it's the assurance you give to anyone else that any of your customers are flesh-and-blood.
I mean, at Communick I offer Matrix, Mastodon, Funkwhale and Lemmy accounts only for paying customers. As such, I have implemented payments via Stripe for convenience, but that didn't stop from getting customers who wanted to pay directly via crypto, SEPA and even cash. It also didn't stop me from bypassing the whole system and giving my friends and family an account directly.