They could set up a separate non-profit organisation (that donates its proceeds to the wikimedia foundation) to sell and manage the ads. Place the organisation in a city far from any wikimedia presence to counter casual contact. Put in the charter than there can be zero personnel overlap between the businesses at any level and that nobody at the ads company is allowed to edit any article on wikipedia or any reason, much less hold any admin credentials . Embrace openness: Publish as much as is practical about every deal, and make sure all ads on the sites are directly referenceable back to the deal in which they were purchased. Publish the names and resumes of all account managers.