So let's say a Junior Suite is sold out on one sailing and people get an email that says "hey Royal Up bid on a Junior Suite."

Those Junior Suites may be currently sold out but Royal is covering themselves in case there are last-minute cancellations. Then when one of those Junior Suites is canceled, Royal Caribbean now has all these bids that are waiting. For example, a passenger in a balcony might bid $100 to upgrade to a Junior Suite. A passenger in an Oceanview bid $100 to upgrade to a balcony. A passenger in an inside paid $100 to upgrade to an ocean view. So if a Junior Suite cancels, rather than that cabin be empty, Royal Caribbean's got $300 lined up because they just bumped everybody up one cabin category due to that Royal Up.

Sometimes there is inventory and they just create a type of auction and whoever bids the highest gets that room.

With that being said, right now, the offers are really aggressive. If you're already booked, I would highly, highly recommend putting the lowest bid possible on the Royal Up, because then you've got an excellent shot of being moved up to that next cabin category.