Foreign exchange is more complicated than that because exchange rates also have a time component: a price of 1 USD is not unconditionally equal to 1.40 AUD just

Foreign exchange is more complicated than that because exchange rates also have a time component: a price of 1 USD is not unconditionally equal to 1.40 AUD just because that's the exchange rate today. If I agree to a contract to pay 1400 AUD in a month's time (at check-in to my accommodation) I'm not OK with learning that I actually owe 1500 AUD, because my agreement was to pay 1000 USD and the rate has gone up from 1.40 to 1.50. Platforms like Airbnb don't always get this right, either, but they can at least specify the deal unambiguously in the fine print even when they display something else, and they should be able to accept payment of my 1400 AUD up front and take on (or hedge) any FX risk themselves.