I reserved a room on Airbnb, confirmed by the host through written messages on Airbnb's system. Nothing about a credit card was mentioned.
Upon my arrival, they showed me the room, which was fine, and they said that they require to have my credit card on file, which will only be charged in case of damage to the room.
Since it was late and I was tired and they already had many positive reviews, I just accepted it. (This was some time ago, and fortunately I still haven't had any trouble with my credit card since then.)
Is this acceptable under Airbnb terms of service? What should I have done in this situation?