In my experience with Anon, people get killed for very standard typical reasons, then they get really upset and blame it on anonymity.
In fact in one case a player was pulling a shady move where we had arranged a 3v1, then one of the 3 tried to play the other 2 of us by using us as leverage to make favorable trades with the 1 getting ganked. So the 2 of us getting played contacted the gank target who had been exceptionally respectful, and we agreed to 3v1 (or 2v1 I guess, as the gank target had been reduced to one outpost) the player trying to play us. Of course, they player trying to play us flipped out and swore off anon.
Also, try offering to share names after the game is over. While it wont force shady players to reveal themselves, it at least creates a small incentive for legit players to be rewarded with good reputation. Might be enough to keep someone who might have pulled a dirty move to play legit instead so they get to be involved in the name sharing part.
Also, try keeping emergency defenses in place so that if things go bad, thetre available to slow/stop the attack. It also acts as a deterent to make it clear to a potential betrayer that if they intend to betray, it will not be a cakewalk.
Also, dont use King.