It looks obvious

The assumption behind projects like Wikipedia is that the masses will write the content and edit it; and that its basically honest use will allow correction of mistakes and misrepresentation. It seems that this concept is now under severe challenge since only wealthy organization can stand a PR attack with budgets like Wal-Mart’s PR budget.  

In order to maintain credibility Wikipedia will have to either appoint fact checkers, step that is in complete opposite to the philosophy of the project, or built mechanism to identify who wrote, or edit content, and allow the users to grade their reliability. This idea isn’t simple to built and maintain but it seems like the only solution to keep Wikipedia somewhat reliable source.

Link:  Wal-Mart winning war against negative articles on Wikipedia

For up to two years Wal-mart lobbyists have successfully waged a war against a fair viewpoint on Wikipedia’s Wal-mart page. Although the Wal-mart page was originally highly critical of Wal-mart, it has slowly shifted to a very positive perspective. Although Wikipedia maintains a ‘Neutral Point of View’ (NPOV) policy, the Wal-mart page is highly biased. Additionally, all criticism has, contrary to policy, practice, and the general opinion of those concerned, been moved to a Debates Over Wal-mart section. Even that page has noticeable resistance to negative points of view about Wal-mart.