For egg accounts, sure, but for anyone with > 1,000 tweets, a real photo and > 500 followers, the level of credibility should suffice for most people. What providers would you add in?
Right, so the users can figure out if the user is credible and you don't do it yourself, got a bit confused there.
If users want people to join their groups then they would add their verification regardless, eg register on the site and then in some bio I could add my SO, github etc...
If users want people to join their groups then they would add their verification regardless, eg register on the site and then in some bio I could add my SO, github etc...