Not that I'm defending the practice (and certainly don't have enough skin in the social media game to do it myself), but it is extremely common to have alts upvote/repost each other on social networks, or downvote brigade someone when you're losing an internet argument.
> Or a small business, but I wonder how much money there is in that.
They call it "hustling" and "growth hacking", and I suppose there might be good ROI on this when you're just starting up and trying to do some "organic advertising" in a niche community/subreddit. Those couple extra upvotes may be the difference between drowning unnoticed vs. staying on the front page long enough to gather initial interest, and spark a discussion that keeps it up for a day or more.
I doubt that even 1% of people using Reddit are using alts to upvote themselves or downvote brigade others. If you have any data to the contrary I'd be happy to hear it.
For some values of "extremely common", because I'm pretty sure most people don't have the patience and energy to do bullshit like that. But a small fraction of people do it a lot.
