HAL and Carnival are the best about providing unexpected upgrades to past pax. CCL creates a number of promotions where it happens at the time of booking. With HAL it happens most frequently with Guar status bookings but they have a little box in the booking engine where you can be considered for upgrades (even if you have an assigned cabin) or decline them if you like the cabin assigned. With most other lines upgrades can happen but are rarer and happen most times with Guar only. Be very careful with Costa if you don't choose your cabin. I recently had three elderly couples that booked an inside Guar above the bunkbed possible category 1A to assure that would not be an issue. What happened? They got upgraded to a Cat 6A which on Costa is a window cabin but back in bunkbeds. They even have some cabins on some ships that have bunkbed configuration in 8A balconies. The call from the ship from an 80+ yr old couple saying they were given bunkbeds and have no other cabins available is not a call any T/A wants to recieve. I was able to purchase two significanly higher category cabins and pay the difference (the agency paid it, not the client or cruiseline) to get two of the three cabin situations resolved. For the third there was no other cabin available even with no shows at the pier. A roll away cot was the only sollution. So be careful about doing a Guar on any Costa ship with these multiple categories that have bunks, you never know what you'll end up with and they won't notify you or your agent if they assign a bunk. You'll find out aboard the ship when it may be too late to resolve.