When I read your post mickto I immediately checked my statement - I've booked a bunch of AirBNBs recently, and AirBNB are headquartered in Ireland I think (for tax reasons, no doubt). Fortunately they come up as "AirBNBAU" or something similar, with no forex charges...
I think you should complain.
I took the advice and sent message. First reply they stood by their decision and said the manager will call me.
I then replied and told them that I will refer the matter (in a way that it is the merchant's fault, because they charged me in AUD in an au website, product printed from Brunswick, Vic)
They then come back with this "we note that the international transaction charges have
been reversed as a one-time goodwill gesture".