I understand that everyone on these boards is honest but, just in case an unhonest poster arrives I would check with NCL and see if you can buy a cabin from a passenger. If my memory serves me correctly I have never known of anyone selling a cabin except a wholesaler or TA.
I might be wrong but before I spent any money I would check it out with NCL.
The reason I think passengers can't sell cabins is as follows. 1. No shows can be resold by the cruise line if you don't arrive on time. If they could be sold then why don't you see cabins for sale by passengers. 2. If you could sell them then insurance wouldn't be as important as it is.
Just before you buy check it out. I would really like to know if I am right.