Simple really....
You cannot stop multiple ID's
You can provide incentive for them to behave within a code of conduct...
An enrollment fee...
Before the play for free party form a lynch mob read on...
It only needs to be a couple of Dollars...
It only needs to be paid once....
It can be later offset against other memberships should knight or rook be taken....
Since they then have something to lose "flaming" "tournament killing" become controllable and BK building expensive...
And if you can afford the ISP service/computer etc 2 bucks will not kill...