Where is the line between opinion and defamation in such a case? If I write a review saying "I was not satisfied" is, in my opinion, just an opinion, I don't have to provide many details unless there is some terms and conditions with the site to provide it. At the same time, when you have a business listed on a review site you have to accept the risk that even bad-intended people can bomb your rating, it's just part of doing business and you cannot expect to sue them all if you don't agree with the reviews, especially if some can be overseas where your friendly judge has no jurisdiction.

I think they just poured gasoline over a fire.