Honestly I can see allied factions doing stuff like that and I perfectly agree that is part of the game, this should and does happen all the time. But having someone join a clan for the purpose to rob them, that should be against the rules. I would think clan leaders no matter the hate they have for the enemy would not allow shit like that to happen.
I know if someone comes to our clan to sell out his own faction by robbing them blind we will go to that clans leadership and let them know about it.
We need to police ourselves or that is what strat is going to come down to.. The dicks of the world taking because they can, and have no consequence for their actions. He will likely just change his name have a new slate. But congratulating him and being happy will last only so long till the game is full of people who are using it to get rich quick and ruining the time and energy the people who want to play it put in.