We made the deal at checkin when we asked. Most ships have a passenger limit, which means some rooms are still available even though the ship is not full of people. Either the ship is not full or a suite has not been purchased, for example. Cruise line gets a little more money from you and you get a deal.
You never know unless you ask, we always do. One other thing, on rare occasions someone does not show up, and no refund is going to happen, perfect storm, you fall into an owners suite for 250. As I said, rare, but it happened to our friends after boarding because they asked and they took their name and cab #, called after sailing and they did not mind moving. We all enjoyed the suite.