> What stops people from setting up and aging (or buying) sockpuppet accounts to the point where they control 10+ or even 100+ flag-capable / vote-capable HN accounts, and then using them as a network to deny or boost certain topics?

It’s a single board with a full-time moderator and almost everyone on it has a background in information technology. These kinds of networks leave very obvious signatures, and the site simply isn’t a big enough place for them to hide.

> This kind of behavior almost certainly goes on here.

Do you have any examples?

Of course, only the site admins would be able to show you actual examples. But this kind of stuff happens everywhere on the internet where you can post for free, so there is no reason to think it's not happening here.