"If you steal from another Telvanni, but still live, then clearly you deserve whatever you stole. Murdering your opponents by magic or treachery is the traditional way of settling disputes. If you win, then clearly your argument has more merit. You may be expelled as in any other Great House, but most Telvanni will not care or even know about it."
Sounds great on paper, but it was not implemented that way in the game. I tried to complete a quest by murdering an opponent and I succeeded but was still expelled from the house and everyone seemed to notice. Could not advance further without paying to make amends.
Would have been a much better game if House Telvanni actually lived up to the hype of being a cutthroat organization with no rules. I wonder why they did not implement it as described in the game?