AWA provides an update on a question about AdWords selling PageRank. In this response, AWA seems to suggest that doing so it not allowed (without makinga direct statement either way).
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OK, I've got some more feedback on this question.
So, advertising to assist with PageRank isn't a problem. Selling PageRank, however, is another thing - and ads/sites are reviewed on a case-by-case basis along these guidelines.
If you're seeing ads promoting the sale of PageRank, then it's possible that those ads have not yet been reviewed/disapproved. At least let's hope that's it. ;)
In any case - thanks for the heads up. This has been passed on to the right folks.