As you work online in any particular niche, you’re going to gain experience and as you gain this experience you should use it in your email credibility campaigns. No one starts off with a CD program or an article with rave reviews, they start with nothing to begin with! It’s important to just build from where you’re at.
As you get established in the niche, you should have third-party websites that comment about your publications. This gives you great social proof as well as credibility that you can use in a campaign.
Even though guest posting is not as popular as it used to be, you can offer to write a post for a respected online website in your niche without putting a link back to your website. This again will pay for itself many times over because the credibility that it establishes for you. Offering to write content for a niche with a small blurb about you without a link should not be difficult to get published on a website. If they do allow a link, then by all means, put it there!
A book is also credibility, and if another source comments on a book you’ve published, that’s powerful third-party credibility.