If you are using an old bookmark to get to ebay.com.au, you may need to update it.
If you use your browser's autocomplete to enter addresses, clear your history to prevent it from suggesting the the US ebay.com site.
If you delete your ebay.com cookies and you are sent to the US site again, you will likely have to sign in. Every time you sign in, check the page address to make sure you are still on the Australian site.
