We were just discussing this with my wife yesterday. The very same story happened to our doula, who's very non-technical and she asked us what to do (we are both engineers). Short story: she had a profile on Yelp, almost 20 5-star reviews from former customers (who spend, on average, 2/3 months with her - so each star is a big deal). One day Yelp! connects with her proposing her to become a paid customer, how could that boost her visibility, etc. etc. Moreover, she has great reviews and it would be good for her to maintain that track record. She declines - also because she is not very technical and she has no idea how much business she's getting from Yelp. Within a month, half of her 5-star reviews are gone and 2 1-star reviews appeared (that she does not recollect as customers - so she reported them).

My get on the entire story is that Yelp sounds a lot like Italian's mafia (btw, I'm Italian) - where "you have a really nice restaurant there, it'd be a shame if something bad would happen to it. But if you pay us, you'd have nothing to worry about."