To be blunt, they're total bullshit. Which is why you never see any evidence, outside of vague hearsay from someone's uncle.
Yelp has a small army of people cold-calling every business in the country to sell ads. Simultaneously and independently, they have a system that filters out bad reviews, all day, every day. Just by chance, someone is going to get called soon after reviews have been filtered. This leads, inevitably, to third-hand stories of someone's Uncle Walter who got called right before/after some reviews were removed.
It could be a small part of those people who are doing this in order to have a bigger bonus. Bad incentive structures that cause bad behaviours is not an unknown phenomenon.
I don't doubt that in an organization of thousands of salespeople, some say bad things. But they don't have the ability to act on their threats. That's the point. Salespeople have no ability to influence reviews.
Also, again...nobody offers evidence of these conversations. It's all hearsay. Lots of accusations, but not so much as a link to a profile page to back them up.
I've read the same or highly similar accounts from other small businesses over years. Did you do this when you worked there? Did your colleagues?