Quote In Local Currency
The solution to all these problems would be to just quote in local currency. Unfortunately most folks want to know how much that is in their own currency, and as soon as they hear that number it becomes the de facto rate. It no longer matters to them that currency can fluctuate up and down.
As an aside I asked at a Canadian hotel once why the difference in exchange rates between what a bank offers and the hotel charges. I got two different answers. One person told me that they typically set it for the month and give themselves leeway to take into account any fluctuations. The other manager told me that a hotel should not be considered a bank and they set the rate in order to discourage people from exchanging or using foreign currency for payment so they don't have to deal with it.
I can see the logic of the second reason. In todays world of credit cards and ATM's you really don't need those services. Twice I've difficulties cashing checks at a front desk because the clerk didn't have enough cash to cover them.