SEO gossips: Google hires spies to report link sellers and manually penalises them

Came across this post on seomoz -

Does Google Employ Link Buying Moles? (see item 7)
Briefly speaking, buying links on topical highly ranking websites is one of the most powerful and easy-to-use methods for website promotion, which is however pertains to the category of grey-SEO techniques and is strongly frowned upon by Google, as this manupulates [...]