As soon as a service becomes a reputed or "go-to" platform for getting tips, reviews and insight - companies instantly try to game it. That's just the way companies and brands online think today - which is why Google has resorted to something like Hummingbird - which ENFORCES that companies think more about actual quality rather than gaming the system.
Yelp's 25% stat didn't surprise me - I was expecting it (and I believe) that it's a lot higher. Wouldn't surprise me if that figure is now closer to 40%. A restaurant will hire SEO Experts to get their Yelp ratings up. They won't tell their chef to cook a better meal or their servers to be more courteous. That's the problem. Unfortunately it's become an extremely KPI driven market on social media - get 10,000 followers, get 5,000 likes, get a rating of 5 on Yelp and what not - and that's why we have to deal with this scum.