First, for those who don't know it, the following is often called the golden rule of diving:
Anyone can call any dive for any reason without any questions.
It means that if someone is uncomfortable with a dive, either before the dive (because of conditions or anything) or during the dive, then the dive is over. Period.
You do not in any way try to push someone to do a dive they don't want to do.
I have done many dives over the years, and there have been precious few that I have called. One was when it was snowing and 20° in New Mexico, and my dive buddy was ready to hop in. Nope. Not me. I have awakened feeling sick on the morning of a dive about 3-4 times. On another occasion, I drove two days for a week of cave diving in Florida, only to get a bad cold after the third day. So I have called dives, but it has been pretty rare.
I have recently encountered a dive operation policy that bothers me--
a non-refundable deposit. I am not talking about major trips, like liveaboards, where you can protect yourself with trip insurance. I'm talking about small, daily dive boats. I can see why they want it. If they had a borderline number of divers to make a trip profitable and one or two drop out, they don't have a good choice. They can either cancel the trip at the last minute, screwing over the other divers who were ready to go, or they can run the trip at a financial loss. A deposit would make sense to them.
That deposit, however, puts pressure on the diver who has decided that he or she is too sick, or the conditions are too tough to do the dive. You may argue that the diver should be willing to pay that cost, but I think a lot of divers would instead choose to do a dive that may in fact put them at needless risk.
I am writing this after choosing not to do a dive I would have liked because the operator requires payment in advance. I am currently perfectly healthy, but I will not work with an operator that is consciously breaking the golden rule of diving.