The clan scam is a scam that involes the scammer telling the victim that he/she will join the victims clan if the victim pays a certain amount of money. But Instead of joining the clan, the scammer will either log out or just walk away.
Scammer is walking around clan camp when suddenly he/she sees someone that needs new members.
Scammer: So, you need new members for your clan?
Victim: Ya, the clan isn't doing too good.
Scammer: I'll join your clan if you want,if you give me 500k
Victim: Great! 1 second.
(The victim and scammer trade, the victim gives the scammer 500k.)
Scammer: Woohoo 500k!
(The scammer logs out)
If you want to avoid the scam, don't give money to anyone that wants to join your clan, they'll probably just scam you.