@DDMJ:
the situation i am thinking of goes like this:
tagFaker entered the game
tagFaker: Hi NOOBS! YOU SUCK!
tagFaker: You all are **********!
Player 1: stfu
Player 2: lol your clan must be crazy to let ppl like you join
Player 1 core dumped tagFaker for x points.
tagFaker was respawned by Player 2.
tagFaker core dumped teammate Player 2! BOO! No points for that!
Player 1 core dumped tagFaked for x points.
....
tagRealmember entered the game
tagRealmember: hey
Player 1: hi

Player 2: hello tagRealmember !!
tagFaker: Hi boss
tagRealmember: Do I know you?
tagFaker: I am in your clan
tagRealmember: who are you=
tagFaker: Faker
tagRealmember: You aren't a member.
tagFaker: I am
tagRealmember: Tell me a thing only I and you know.
tagFaker left the game
Player 1: the idiot is away...
Player 2: Realmember, why is that stupid twat in your clan?
tagRealmember: Idk him.
Player 1: You should know your clanmates. I will tell an admin what he said to us.
Player 2: I will complain at the forums.
----------------------------------------------------
You understand the problem? Auth doesn't help a lot here and isn't a real alternative. When the guy goes to the next server, the same problem starts again. and when the faker is an imposter at the same time, maybe some other player's IP gets banned because of him.