Brett - Whilst I don't necessarily agree with Drew, I can see that there will be Mach 3 users to whom a failure in their system will lead to serious financial loss to them, whereas I, as a hobby type user, can afford to wait for a result.
It seems to me you should offer several levels of support - speed apparently being of the essence, and, having purchased one of these levels of support, we can ring in and, perhaps, quote a code. Whem you are analysing the first calls, the code then gives you the order in which to answer.
It may be, on some days, the 5 cent option gets the 100 dollar service, because there are no other calls. On other days, everybody has to be strictly dealt with on the basis that, as Drew says, those who pay most get the fastest service.
To my mind, a premium payment initially - which gets you the "speed" code, but after that I think a standard charge for the actual time used for the problem. My problem might be just as important "to me" as Drews is to him. He pays a premium, therefore gets the first service, I dont, therefore have to take pot luck. After that everybody pays the same for your expertise.
This, I think, is fair and understandable to everybody.