Total number of links from other pages to yours. Each time someone links to your site you get more credibility from the search engines. If the website linking to your site has a very high Google ranking, then you'll get even more credibility because they're already considered a trusted source.
Recommendations: Look for relevant websites to link to your site to give you more credibility such as:
“Spartan Spark helped me take my site, that was already 7 months in development and basically re-build it in 7 weeks - and rocked!” -Mitch Solway - President, Single Parent Love Life Inc.