How do the bans in this game work? Can you ban their cd-key or just their character?
They do key bans. Anytime you get banned for anything, it's all of your characters. Only way to get back is with a new CD key and even then a suspicious enough dev might decide to look up IPs, as we know they track IPs as well.
Basically this isn't some MMORPG where people can cheat for months and not get caught. Good players, in particular, notice autoblockers and admins aren't that rare.
It's also not an FPS where you can aimbot and people can't really be sure if you're doing it or not -- blocking is up close and personal and a little too obvious.