If you are traveling on a Tourist Visa to Australia, then you can not work while in Australia. If they catch you, the fine is up to $10,000 and you will be deported. [
www.findlaw.com.au] Try to find Post-Security shops at the airports you will be leaving / arriving / transiting in the US. You MIGHT also be able to do shops in the duty free shops post-security in Australia, but check carefully before you try that.
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008