B.J. Fogg and his associates at Stanford are looking at how you can make computer experiences more persuasive. Out of these efforts come principles for making your web site more credible.
Just one good take-away out of many: Typographical errors and broken links hurt a site’s credibility more than most people imagine. So one of the guidelines for web credibility is this: Avoid errors of all types, no matter how small they seem.
It is worth checking out the rest of the principles. While some may appear obvious, they have been backed up with strong research. The principles are published here.