In January, Google began to send out webmaster tools notifications for selling links. Now it appears that Google is sending out notifications for buying links.
The email notification reads:
Dear site owner or webmaster of http://www.domain.com/,
We've detected that some of your site's pages may be using techniques that are outside Google's Webmaster Guidelines.
Specifically, look for possibly artificial or unnatural links pointing to your site that could be intended to manipulate PageRank. Examples of unnatural linking could include buying links to pass PageRank or participating in link schemes.
We encourage you to make changes to your site so that it meets our quality guidelines. Once you've made these changes, please submit your site for reconsideration in Google's search results.
If you find unnatural links to your site that you are unable to control or remove, please provide the details in your reconsideration request.
If you have any questions about how to resolve this issue, please see our Webmaster Help Forum for support.
Sincerely, Google Search Quality Team
As you can see, the specific line "unnatural links pointing to your site" versus the old notification that read, "unnatural links on your site pointing to other sites."
That being said, with these new notifications, Webmasters can clearly know if they have links pointing to them that has a direct impact on their rankings.