On reddit, all they have to do is create an account. They can attest that the account is official wherever they want.
The issue that arises with this article is that the people using reddit perceive paid comments as an abuse of the channel, especially when the for pay nature of the comments is obscured.
An astro-turf user is by definition misrepresenting themselves. They gain credibility by presenting themselves as unaffiliated with the candidate.
The Hillary supporters claim this is "required given the money being raised on the other side" - $2B is a figure thrown around, and that not doing this is essentially ceding the field.