I don't use Yelp so my opinions are both irrelevant and formed entirely by what I've heard from others. I'm not sure I believe Yelp hides/shows reviews based on whether businesses are willing to pay but I'm not sure I put too much weight in the above posted link either.

If Yelp's review algorithm has nothing to do with advertising spend then it should be fairly easy to have someone from PwC/Deloitte/E&Y look at the algorithm and issue a letter saying advertising spend isn't a factor. I'd give a lot more weight to a third-party review than I do the Buzzfeed article (not Buzzfeed News) and academic study on the ethics and incentives behind review fraud that Yelp has cited.