We have banned people in a few cases for serious $BigCo astroturfing but there's always a grey area in the Venn diagram around "PR operation" and "overzealous fan". You can't tell those apart without a smoking gun and those are hard to come by. Fortunately, from a moderation point of view it's a distinction without a difference because the effects on the site are the same.
Also FWIW, my sense (and we do have circumstantial evidence for this) is that even when these things are PR, they're somehow haywire (e.g. a contractor gone rogue), not official strategy, and if high-enough execs found out about it they'd probably shut it down. That's just speculation though; informed speculation, but not highly informed.
I do not want to single out a single company, but would like to use this particular example to ask you the following: Please keep in mind the level of manpower and persistence, some of these corporations can call upon for their strategic objectives..
In 2020 Microsoft had, apparently, 106 lobbyist companies working on its behalf: https://www.opensecrets.org/federal-lobbying/clients/lobbyis...
and 94 in 2021 https://www.opensecrets.org/federal-lobbying/clients/lobbyis...
Looking at the website of some of these companies, offered services include and quoting: "Third party influencer outreach" :-)
I think social media (sorry for calling this site that) vote manipulation detection will be one of the defining problems of the decade.
I can attest to this: at one of my old companies a post related to us ended up getting removed, just because so many of our engineers (entirely independently of the company) voted or commented on it. After that there was a very strict instruction from the company _not_ to engage with any posts about us...