I have been in a guild and it randomly got hacked and every member got kicked. We were just about to re-recruit all the members when I suddenly saw that a Perm that just came online recruited the hacker again. He was blacklisted but the Perm didn't know it. So I suddenly had a random idea:

There should be a Guild Ban!

It's easy: It should be a right for the leader only or a right to give away like recruit or kick right.
If you have the right you can just click on the player you want to ban, go on more actions and press a button like 'Guild ban'
Of corse you or anyone else with the right can always unban the player with for example 'Guild unban' (just like block and unblock).
As long as the player is banned from the guild he is not recruitable to the the guild he is banned from.
On this way you can keep your guild clean from all the players that you don't want and people can't just change their look and name and get re-recruited as a "totally different person" that they seem to be.