I admit I haven't read the whole thread but some don't seem to understand how this is done.
The final bill you get isn't final. That's a start. They can and often do post to your account after you leave the ship - there is nothing unusual about that - they do it.
If there is a balance owing when you go to leave the ship when you put your card in the machine it will ding at you and you can't leave. You must go back to the service desk.
If they post after you leave the ship it will show up on your credit card. The only one's they haul back are cash customers because of course, they can't get any money from them once they've left.
The OP is correct all the way and why the rest have berated him is beyond me.
Celebrity Constellation - March 17 followed by Celebrity Reflection - March 22
44 cruises - too many to list however cruiselines are in no particular order:
and some unknown tub
Yes, I'm a Royal Chump and proud of it.