We very rarely get involved with move up, but if and when we think we might, I note the fares for the upgraded stateroom(s) I would consider at the time that I am booking the original stateroom selected. I then follow that category(s) fares from that initial booking time, and the bid I would enter for any upgraded stateroom would typically be lower than, but would not exceed the difference between what I paid and what the lowest fare offered was for that category. Once entered I would not change it. If I get it, great, if not, no loss. But in this manner I am assured I would not overpay with the bid.