Link building is one of the most important things a webmaster can do. On-page SEO factors are important, of course, but it is difficult to achieve high rankings for most search terms today without some kind of inbound link strategy. That involves searching out places to put your links and ensuring that you have the proper anchor, that your links point to the right pages on your website, and that you don’t do too many too fast.
Because Google places such a high priority on inbound link quality, it is necessary to evaluate your linking strategy to ensure that you are helping, not hurting, your website. PageRank is based in large part to the number and quality of inbound links. When one site links to another it is considered a vote of quality.
Because of this, when you link to someone else’s site from your own you are essentially helping them rank better in the search engines by providing the proper anchor text and linking to the right page from the right page on your site. That link could potentially earn them money. That’s why many webmasters have started selling links and link buying has become its own industry. But if you buy and sell links and Google finds out then you’ll be penalized. It’s a never ending game based on one fact: Links are like currency. Pure gold. Money in the bank. Build enough good ones and you’ll earn your keep.