I am pleased to say that my experience has been the same as that of cbm32. Know your charter company, and communicate with them ahead of time. Most will be candid with you about their policies. Another way to avoid this issue is to travel in a group that itself is large enough to guarantee each trip "goes." (though Debbie and I prefer to travel a s a group of two, and sometimes four). Obviously, policies will vary from location to location, and culture to culture. I have found that when I prepay for my diving, there is a much lower chance of cancellation than if I am paying at the time of the dive or at the end of my dive week. After reading the thread, I feel blessed to have never been "cancelled for lack of interest."
DivemasterDennis
DivemasterDennis