The consequences for false negative and false positive are not the same. If there is a (fake) negative review (that seems real), the plenty-of-fish rule applies (at least for me). I will avoid her if there is an equal choice without a negative review. This may not be fair. But I don't care, I don't answer to an employment tribunal - I just want a great punt, and statistically speaking, this increases the chances. But I never learn that it was a wrong review, oh well.
If there is a (fake) positive review and I visit and it is bad, I am out the cost of a punt. And I write a review stating my experience. So everyone finds out. It still doesn't prove the review was fake (if it was about service, as that can change), but now in any case there is balance.
As others have said, it is way better than these two extremes. On the regional boards, one quickly gets a feel for good posters and so on. And the plenty-of-fish rule does not work very well for regional agencies. There are not very many, and someone seems to complain about each of them.