In a decentralized system, users could have various "vouches" for the authenticity of their messages. A trusted user could vouch for a new user, and/or the use

In a decentralized system, users could have various "vouches" for the authenticity of their messages. A trusted user could vouch for a new user, and/or the user could go through various types of third party verification, such as phone number, ID verification, or other verification, and then the third party could vouch for them on that basis. You could even have monetary vouches, where a third party vouched that the user paid a certain amount of money, solved a captcha, or solved some computational problem. The user could be in control of what measures would be required to reach their screen. As it stands, social media essentially incorporates a combination of trusted user vouching (you can see who is a friend of a friend), and monetary vouching (advertising).