In earlier days, credibility giving sources were limited and centralized.
But now, the credibility sources are more decentralized and are more freely accessible.
The following are the widely used credibility sources
A track record of having started one or two successful businesses.
Industry-related blogs with well-written, lively, detailed posts, which receive many comments and tweets/likes/shares per post.
Large, legitimate, real followings on Twitter, Facebook, YouTube, and other social media networks.