• If you score a re-pack, slag the original releaser for their unfathomable incompetence in the nfo

Pretty much nailed it, but for anyone out there thinking "hey I can do that"....

Point #1 is hard to do these days as a solo effort. A lot of these piracy groups have massive manpower backing them up, whether it's a paid business or just a bunch of like-minded enthusiasts.

Point #2 is a little more doable, but you'll spend all your time doing that to keep up with the release schedule of these groups. That or you'll have to rubber-stamp your releases without much quality checking, which will affect #3.

However, Point #3 is where small enthusiasts can absolutely shine. A great example (though possibly on the more involved side) would be Adywan, who made their name focusing entirely on releasing maximum quality Star Wars releases, recuts, remakes, and remasters. There's maybe a few dozen releases to their name, but mention that name to any piracy-aware Star Wars nerd and they will know it.

For as much content as the big names cover there's lots of stuff that falls through the cracks, whether it's entirely absent or just present with sub-par quality. Despite how large the Star Trek fanbase is there's basically one copy of the non-remastered version of The Original Series floating around out there, and it's a rather ancient encode.

I guess I was asking how do these people, make the torrent say their username?

You just name the torrent with your username when you make it. They mostly follow an agreed common format to include all the relevant information in the torrent name like: Name.Of.Movie.Year.Resolution.Source.Audio.HDR.Codec-Group

And how do peers know it comes from them?

This is usually by trusting the tracker that indexes the torrent, which is usually only possible with private trackers.

PTs have scrict requirements for publishing torrents on their tracker and will tie torrents to a user on their website so that it's impossible for other users to impersonate a group/user release name.

On public trackers, people can just lie since there's no limits on publishing torrents and its up to the mod team to handle fake/bad torrents. Piratebay used to actually be pretty good at this with verified usernames but now I'm not so sure.

The easiest way is to join a PT which will report the same torrent hash for the same torrent on a public tracker. If it's identical to the PT torrent, that means its from the genuine group/user.

Every torrent starts with somebody. Someone repackaged the goods, or ripped the stream, or whatever. The original uploader can call the file(s) whatever they want.