Qantas has a DCC option on its Australian site, which is selected by default, when using a non-AUD card. I've included a side-by-side comparison:



The DCC price includes the card payment fee, and the listed conversion rate is 3.99%, currently at 0.828 AUD/USD. However, Visa's current exchange rate is 0.794621 AUD/USD, so the DCC spread is more like 4.2%.

Opting out is easy, but I imagine the default selection of DCC catches people who are unaware of the option.