After a negative review of a Medialink Wireless-N Broadband Router gained the honour of becoming the "most helpful negative review", rather than selling a better product, Medialink responded by threatening to sue the reviewer for "...an illegal campaign to damage, discredit, defame and libel...".
Maybe they're hoping that this sort of personal attention will make people want to do business with them?

http://www.amazon.com/review/R1YBUCWN9AWPVW/ref=cm_cr_pr_viewpnt#R1YBUCWN9AWPVW

This is a growing trend.  A woman in Fairfax was sued $750,000 for a one-star review on Yelp: http://www.foxnews.com/tech/2012/12/05/woman-sued-over-yelp-review/, a couple had their credit rating wrecked by a surprise fine of $3500 by KlearGear for a negative review. http://consumerist.com/2013/11.....t-right-or-get-sued/

As long as a person is writing about their own experiences and stating facts, these reviews should be protected by our rights to free speech.  Then if a vendor has a problem with what you say, it should be their own responsibility to ensure customer satisfaction.  In the case of the Fairfax woman, she shouldn't have stated or implied that the contractor stole her jewellery without definitive proof.  If he neglected to do work that was part of their contract though, he should be held accountable, and she should be able to warn others that they could run into the same problem.
With the huge online market these days, there clearly needs to be a set of laws specifically aimed at protecting online consumers from this kind of stuff; a "non-disparagement clause" shouldn't ever be allowed, except where normal slander or libel laws would apply.  It would be difficult to enforce these laws while keeping them from being abused at the same time, but there has to be a way.  The vendor is always free to publicly tell their side of the story too.

It's hotel policy to charge for bad reviews.  This is what a couple were told after being dinged an extra £100 by the hotel they visited.  http://www.bbc.com/news/technology-30100973

Quoted Text

The hotel policy, contained in a booking document, reads: "Despite the fact that repeat customers and couples love our hotel, your friends and family may not.

"For every bad review left on any website, the group organiser will be charged a maximum £100 per review."

So this is slightly different from the previous posts in that it's not a matter of suing the customer, but just outright charging.  Does a company have the right to charge the customer whatever they please, especially if such charges are listed up front?

It's absolutely not right, because it essentially absolves the vendor from any responsibility to provide good service.  On the other hand, recognizing that a vendor had no desire to be accountable for the quality of the service or product they provide, I would choose not to deal with them in the first place, and maybe even point the fact out to others.