On Reddit, where downvotes are anonymous, my niche sub (20k members but far fewer active) would continually get someone who would come in and downvote every single comment in an entire post. The time that it started and stopped was fairly obvious too b/c like in a Help & Questions megathread with literally 1000 comments, all of the replies would have a baseline value below the starting one (i.e., they would show 0 rather than 1), up until it stopped after which point they would all start at 1. That’s a pretty clear indicator that they were subverting the rules of Reddit. As a moderator, I repeatedly complained to the Reddit admins, who did not seem to give a shit.
I even had screenshots of people on an associated discord server calling out for such brigading attempts. I offered them to the admins, who never took me up on that. It also happened in a much larger, I guess you could say parent sub of 200k members. Hundreds of thousands of people getting downvoted… b/c of one unhappy kid, or someone acting like it.
At least here in the Fediverse we have tools at our disposal that were not available on Reddit. e.g. if you were to block all of those people, I think they cannot vote against your future posts any more? Though it could also be due to a simple misunderstanding of how to use Fediverse tools. And for someone who made their own instance, you could literally adjust the rules - I would guess? - so as to only show the results of voting e.g. for accounts older than X days, or only by members of that community, or something. Though that would take significant effort, both up-front and then to stay in compliance with future Lemmy updates if it was not integrated into the main code, and it would only benefit members of your specific instance.
For someone who so rarely downvotes anything - I usually either just block a troll entirely or at least ignore someone who looks like they may be having a bad day yet feels the need to share that with the entire world - I might not be providing much perspective here! But I hope these thoughts at least were somewhat interesting.