Why I ignore Amazon's "helpful" ratings ...

I think this sort of thing is pretty common, even when it doesn't involve bribery ...

Slashdot | Belkin's Amazon Rep Paying For Fake Online Reviews

... recently discovered that Belkin's lead online sales rep, Michael Bayard, has been secretly paying internet users to review his company's products favorably on Amazon.com and other websites like Newegg, whether or not they've ever used the devices. Bayard instructed the people he was paying to 'Write as if you own the product and are using it... Mark any other negative reviews as 'not helpful' once you post yours.'..

I always read the negative reviews. I never bother with the "helpful" rankings because they're often obviously gamed.

I kind of figured this out when I realized that my positive Amazon reviews were always "helpful", but my negative reviews were often "not helpful".