It becomes important for the webmasters to review the Google’s Webmaster guidelines so that they do not violate the guidelines. Webmasters may place text link advertisements on the site but only after they have added the “no follow” attribute on the links. This would save their sites from getting penalized by Google.
Not only the sites selling links are penalized but the sites buying links are also penalized in the same manner. Hence, it is necessary to avoid these sort of practices which aims to manipulate the original ranking algorithm of the search engines. If you want to make your site succeed in the long run then its better to follow white hat seo pratices and care for your user.
Adding advertisements by way of Adsense, Chitika, Adbrite, Kontera etc won’t harm your site because they work well in hiding the links from the search engines or add a no follow attribute to the links be default.
Have a look at this video by Matt, explaining why paid links are a violation of Google’s guidelines:-
Also See:-
Search Engine Optimization or Search Experience Optimization
How to Create Backlinks That Google Loves
Backlinks
How to Rank in Google
How to Design Seo Friendly Web Page
How to Make Your Website More User Friendly
Benefits of Seo
I’ve had offers from sites wanting to pay me for links, but i always say they have to be NoFollow suffice to say, i never hear from them again. DoFollow and NoFollow can be a little confusing to new bloggers.
I always have my own rule that paid should always be 'NoFollow' and i stick to that. 🙂