I am not offering an opinion on this. I am just noting what Glassdoor itself has to say about this.
There are enough ways to put the thumb on the scale that you can honestly say that you don't have a delete bad review button, yet money can still strongly influence how positive or negative an org looks on a review site.
The followup here, strongly suggests other un-related people have been called, even cold-called, and offered by people puporting to be glassdoor, to wipe the problem.
I agree you aren't offering an opinion and I value that. I would also value some commentary to my note: What do people think, about what people said on reddit, and said here, regarding this, and what glassdoor said in September 2019?
I know what I think: I do not believe this policy is well enforced, and I believe the posters who say they were invited to pay to clear their record. You notice they do not have "report breach here" links on that FAQ item. They do disclaim it has legal force.
It may of course be unscrupulous non C* staff, or it may be intermediaries mis-representing their role, e.g. SEO leeches.