As far as CRM goes, and concerning corporate stuff, and this is what I teach in my courses, this is one business where the customer is not always right, and there needs to be a fine line drawn (politely!) between the requirements of the customer, the management and the pilot.
Why should the fact that the customer stands to lose 100K (or whatever) if you don't get him to a meeting on time become part of your problem? Your problem is to get him there safely - the consequences of that don't come into it, assuming you've done your job properly and advised him that there are no guarantees and that he will still be billed for an abortive flight.
I had to struggle a bit at Alton Towers to get that established, but there was no problem at JCB, or any other place that I worked.
The sooner we stop taking on customers' problems as well as our own, the better off we will all be.
In declining something, offering an alternative solution is a good way of sweetening the pill.
Phil