I worked at Yelp in 2018, and the allegations were there, I would be extremely surprised that a secret like this could be kept if it were true. It was generally a pretty open culture which lots internal open cynicism. There was just 0 evidence or even rumors internally this is true. I believe it's way more likely that the system is large enough to generate outliers that believe they're being targeted.
However, hyper aggressive sales reps were there and while I don't have specific details, I know their methods were the cause of at least some people not comfortable staying there. They however would not have access to things like reviews.
Is it possible that sales reps were using the publication of negative reviews by others as a tip-off of which businesses would then be more likely to purchase the service by which negative reviews could be removed? If so, the timing of those sales pitches along with negative reviews could make it seem like this is what was happening.
However, hyper aggressive sales reps were there and while I don't have specific details, I know their methods were the cause of at least some people not comfortable staying there. They however would not have access to things like reviews.