Even with heavy automated moderation, if you really want to manipulate ratings data, it's just not that difficult until you can grow a community which has a checks and balances system. User reviews just take up too much time for the companies to moderate, they must turn review quality to the actual users as well.
Everyone already knows how to manipulate Alexa data. For a while, it was beneficial to manipulate the Alexa data for several purposes (and some still do it to sell links/advertising so they can claim a higher visitor volume than actually occurs).
However, there are several communities which give us some hope in this area.
When user reviews first stated on many site, most of the reviews were written by the owners, authors, publishers, and friends for their products. This created artificial rankings for many products. This will be the first step we see in local search - the artificial rankings for restaurants. Even now, it's easy to manipulate Yahoo Local, as the majority of restaurants still consist of 0-1 reviews.
As community sites grew, more people wrote reviews, and products & services started being rated based on real reviews and not artificial rankings.
This still wasn't a perfect system as there was no review quality, and the data could be manipulated by people dedicated to making their product always have a high review. Then the 'was this review helpful' was born.
This helped publicly show what many people thought of the review quality. The checks and balances system has served many review sites well.
Amazon took this a step further with Listmania. The idea was good (and to my knowledge, there is no affiliate IDs associated with any products) and the lists were truly altruistic. Again, the major checklist for a good list is the 'rate this list'.
With local search and user reviews, we're going to see another growth process where at first, the rankings are easily manipulatable. The question will be, can these local search engines/portals bring together a community that will impose checks and balances so that the reviews lend true quality to the community.