I saw a thread today where a poster claimed that NCL lowered their fares when a promotion was over, while others chimed in and claimed that their cruise's fares either had not gone down or in fact had gone up.   I have also had debates here with people regarding the best time to book.   So when is the best time to book, and why do the fares jump up and down?   The short answer: It depends.     Computer Predictive Modeling   It is important to understand that there is not a human bein