I'm surprised people think they wouldn't. They have the perfect hideout. Whatever the case they can always blame it on the "algorithm," and short of auditing their source code, nobody can really prove them otherwise.
[Full-disclosure: I'm friends with a good number of Yelp engineers who I expect would leave rather than take part in these such things, but I don't know any more about their codebase than any other non-Yelper.]