It's a little funny to me that you mentioned Yelp. I have had a bunch of 5 star reviews posted by customers on Yelp only to have the reviews moved to their "Not recommended" tab by their software that can't be reversed by anyone. Mysterious, I don't think so. It just so happens that I noticed a trend and then confirmed it.
After each 5 star review I received a call from the Yelp "advertising representative" mentioning how my business page is in a fast growing category, popular search, or asking me if I had spoken to a Yelp rep before. Then they try and pitch some version a sales pitch, unconvincingly, and then I explain that I'm not interested in their add support or paying them to move me up their totem pole. Then I politely ask them about my 5 star reviews getting moved by their software to which I get a canned response about how they can't move my reviews and algorithms blah blah blah. The next day, sometimes faster, the review that was legitimately from a thankful customer of mine was moved to the before mentioned "Not recommended" tab. Since I verified this whole process with the last 5 reviews I have gotten I have stopped asking customers to post reviews there and instead post them on my Facebook page where I have control of them.
Yelp is a total scam. So many lawsuit's it is crazy. And I've see the exact same thing happen to reviews I've left. One was even deleted.