The answer, yes, is the correct one.
No Customers ever tip with a direct billing, never has happened, office would never even ask a Customer about tipping the crew. The only tips I or any other crew has gotten was at the end of the flight saying goodbuy to the passengers. If you have received a tip, did you share it with the office? If it weren't for the office, your tip would not have happened in the first place. I had a dumb*** start telling the office girls about the $1k tip we got, I about flew accross the room to choke him.