Fees are charged by Carnival, right?
In the same way that your mechanic charges you for the parts he install on your car: it's a pass-through. He pays the wholesale auto parts house for your part, he charges you what he paid.
I agree that if this transaction happened as the OP said it did
Of course it happened the way it was said; but the mechanics of it are completely misinterpreted, and the wrong parties are getting blamed, and people are filling in the blanks with what their biases suggest rather than employing Occam's Razor to it.
I also do not believe that Nassau Port Authority changes its docking fee 20 times a week. I believe they charge a cruise ship a fairly stable fixed rate that doesn't change that often - in total amount. If you've got a ship with 'X' gross tonnage ... then the docking fee is $Xn,000. But I also believe that they require that fee to be collected the way their law says it muct be collected, just like all governments everywhere do, and the calculation for that method of collection is imposed upon all cruise lines which would use the port of Nassua as a destination.
My employer doesn't set federal tax rates, but my employer calculates withholding anyway. And the withholding can change dramatically each time I modify my W2, or alter my 401k contribution ... the IRS gives my employer's payroll department the calculation they are required to use to compute withholding, taking all those factors into consideration.
The factors I believe go into the fee/tax for each new booking are current passengers booked pct, passenger capacity, and time left until sailing. But that's just my guess, and there's probably more variables besides.
SIG: If you're going to create the drama, at least supply the popcorn.