Hack Report
If you see a player using exploits or something like the only thing to do is report the player through in-game tools. This way GMs and staff can deal with them.
But if you can’t see or get the player abusing, as you mentioned, but know about some exploit or something that can be exploitable you can report it to exploits@arena.net. Just to note that, as stated by a dev, that email is for reporting exploits, hacks and stuff, not to report players.
Also, be careful about naming and shaming on forums, it’s frowned upon and not a good thing.