Thanks for reminding me about the principles that are in the Cialdini's book. There are a couple of elements that I could extend on this article. Something that you can use for social proof online is lots of testimonials. If a lot of popular credible marketers have their name behind a product, then many prospective buyers will associate the quality of the marketer with the product. In addition, to help establish authorities, try to collect as many "badges" to place on your website. That's why marketers place "as seen" on ezine articles, Digg, Google, Yahoo, and etc on their website on clickbank. Some people will think that "oh wow" this website was featured on this network, so it must be an authoritative website.

Doug