It seems now that a lot of people that sell links get their PR lowered. But it also seems that the sites that sells links dont lose position in the search results or get a lower amount of visitors. So I want to discuss if Google think it is fine to sell links, but thinks its not fine to earn money as a result of high PR as Google think PR should just be a tool, not a money maker.
Google 'might' think that selling links is bad for their SERPs, and for Adwords... So, selling links, Yahoo ads, all other ads are ... Everything what is a tool, can be a money maker.