It's a pretty expensive undertaking. You have to be a subscriber (at non-trivial cost) to be a member/reviewer. The vendor would have to create multiple puppet accounts at $20/pop to shill up reviews. But, what of all the
other actual reviewers that will write bad ones? You tend to see patterns in the reviews and, when a shining review of a vendor leaves me skeptical, I always look at the members' other reviews to see if they left at least 2 or more. If they did, then I suspect less that they're in cahoots with the one vendor.
The Limbaugh thing is unfortunate, that's true.