My personal statement is a plain "Don't sell links for passing PageRank™. Never. Period.", but the intention of ad space purchases isn't always that clear. If an ad isn't related to my content, I tend to put client sided affiliate links on my sites, because search engine spiders didn't follow them for a long time. Well, it's not that easy any more.
However, Matt Cutts 'revealed' an interesting fact in the thread linked above. Google indeed applies no-follow-logic to Web sites selling (at least unrelated) ads:
... [Since September 2003] ...parts of perl.com, xml.com, etc. have not been trusted in terms of linkage .... Remember that just because a site shows up for a "link:" command on Google does not mean that it passes PageRank, reputation, or anchortext.
This policy wasn't really a secret before Matt's post, because a critical mass of high PR links not passing PR do draw a sharp picture. What many site owners selling links in ads have obviously never considered, is the collateral damage with regard to on site optimization. If Google distrusts a site's linkage, outbound and internal links have no power. That is the optimization efforts on navigational links, article interlinking etc. are pretty much useless on a site selling links. Internal links not passing relevancy via anchor text is probably worse than the PR loss, because clever SEOs always acquire deep inbound links.
1. Implement the change recommended by Matt Cutts:
Google's view on this is ...selling links muddies the quality of the web and makes it harder for many search engines (not just Google) to return relevant results. The rel=nofollow attribute is the correct answer: any site can sell links, but a search engine will be able to tell that the source site is not vouching for the destination page.
2. Write Google (possibly cc spam report and reinclusion request) that you've changed the linkage of your ads.
3. Hope and pray, on failure goto 2.
Tags: Search Engine Optimization (SEO) Google PageRank™
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