be sure you really want to take a particular tour... once you buy it you own it..
the only way to get your money back is to be excused by the ship's doctor at a cost of 45.00.. i lost over 200.00 to a shady dfast talking... rep of royal olympic cruie lines.
bummer!! I found that many (at least the ones I booked) didnt' require anything in advance, just a relatively good faith committment that you'd be there. in both cases, two of the people we were booked to go with decided to opt out at the last minute. Both tour companies were fine with it. One company who only had the four of us booked said they needed to try and find a few others at the dock and within minutes, they had 4 other people, so there were six of us in total. Just like there are shady and unscrupulous companies out there, I also think there are honest and exceptional ones. Too bad you came across the former.
Let me add one other thing... I don't mean to imply that you should book with a company and then just blow it off. If you have a true faith belief that you will go, you should book. Otherwise, take your chances and try to book them on shore. Otherwise, you're wasting the company's time and resources. Having said that, sometimes things can come up and cancellation is required. A good company will understand that, but you as a customer should have integrity when booking.