The following are examples of link schemes which can negatively impact a site's ranking in search results:

Buying or selling links that pass PageRank. This includes exchanging money for links, or posts that contain links; exchanging goods or services for links; or sending someone a “free” product in exchange for them writing about it and including a link Excessive link exchanging ("Link to me and I'll link to you") Linking to web spammers or unrelated sites with the intent to manipulate PageRank Building partner pages exclusively for the sake of cross-linking Using automated programs or services to create links to your site Here are a few common examples of unnatural links that violate our guidelines: Text advertisements that pass PageRank Links that are inserted into articles with little coherence, for example: most people sleep at night. you can buy cheap blankets at shops. a blanket keeps you warm at night. you can also buy a wholesale heater. It produces more warmth and you can just turn it off in summer when you are going on france vacation. Low-quality directory or bookmark site links Links embedded in widgets that are distributed across various sites, for example: Visitors to this page: 1,472 car insurance Widely distributed links in the footers of various sites Forum comments with optimized links in the post or signature, for example: Thanks, that’s great info! - Paul paul’s pizza san diego pizza best pizza san diego Note that PPC (pay-per-click) advertising links that don’t pass PageRank to the buyer of the ad do not violate our guidelines. You can prevent PageRank from passing in several ways, such as: Adding a rel="nofollow" attribute to the
tag Redirecting the links to an intermediate page that is blocked from search engines with a robots.txt file The best way to get other sites to create relevant links to yours is to create unique, relevant content that can quickly gain popularity in the Internet community. The more useful content you have, the greater the chances someone else will find that content valuable to their readers and link to it. Before making any single decision, you should ask yourself: Is this going to be beneficial for my page's visitors? It is not only the number of links you have pointing to your site that matters, but also the quality and relevance of those links. Creating good content pays off: Links are usually editorial votes given by choice, and the buzzing blogger community can be an excellent place to generate interest. If you see a site that is participating in link schemes intended to manipulate PageRank, let us know.
We'll use your information to improve our algorithmic detection of such links.