hey folks, just thought I chip in to this thread's discussion. may or may not apply to this particular scenario, but here goes:
my wife has been charged with some transaction fees for "international purchases" by her card's bank (Comm Bank). initially, she didn't think too much about it, as she thought she may have inadvertently selected another currency instead of Australian dollars. but when other transactions started copping the same charge from the bank (even after she was certain that she selected AUD as the currency to be billed to her card), she did a bit of digging on the internet and found out that Comm Bank started this business of charging for international transactions at a rate of 3% per transaction as of August 2016. the other banks have done likewise, and Westpac was in fact asked to refund the charges they levied initially as an adequate notification was not sent out to their customers. Comm Bank did theirs via a small notice at the bottom of their statement, and apparently that satisfies legislative requirements.
anyway, back to this charging business. it apparently is the buyer's responsibility to sort out where the billing takes place, even though the website could have a .au suffix. the information isn't that easy to find on most websites, and you would assume that if it's a .au suffix... that it's based in Australia. previous transactions with the same websites in previous years have not been affected by this international surcharge from the bank.
funnily enough, it's not consistent. we still haven't been charged by some sites (AirBnb comes to mind). but I don't want to jinx us just yet.
I on the other hand, haven't been charged with this international transaction fee nonsense. mainly because I've used PayPal, but for some purchases like Spotify/Netflix, I haven't been levied with the charge (for now, until American Express starts figuring out how to milk me for more money!)