I'm local to this case, so I may see when it's on the docket and watch it.
In my opinion, because of the permanence of online reviews and their wide availability, theres a difference between telling your neighbors "that contractor sucks" and posting on Yelp. But I don't think they rise (liability-wise) to the level of a review in a newspaper or magazine, by someone who is paid to be a critic.
If one clearly distinguishes between facts and opinion when writing a review, and sticks to the true facts, one should not have to worry.
Example:
Mr. Smith was frequently late, arriving after 10 AM on most days. The toilet initially delivered was not the toilet I had specified. I was not happy with the quality of the installation of the plumbing fixtures.
Two facts and an opinion, and it's pretty easy to tell which is which. As long as I can back up the facts, I should prevail.