Purchasing in Australia yet incurring a foreign transaction fee

Where did you get your ‘real rate(s)’? Published rates are for bulk transfers, not consumer retail exchange. Today OANDA pubishes

Australian banks are notorious for providing very poor exchange rates in both directions.

Buying $USD is most likely to be around the minimum (worst) rate, noting rates change by the second +/-. My fee free accounts rate has always been the Visa/Mastercard rate of the day/moment. Another topic you might be interested in is