The "Australia ONLY" filter does not mean what you would think it does. It's actually quite misleading.

It just means posts ONLY to Australia. So a Chinese registered and located seller who mails only to Australia will show up if you use this filter.

On the other hand, a seller who is physically located in Australia and who posts to Australia and other overseas destinations will NOT show up when you choose this filter. Because they do not post to Australia ONLY.

There was some discussion and experimentation done on this a while back.

Have a look at this thread.

https://community.ebay.com.au/t5/Selling/Australia-Only/m-p/1819726/highlight/true#M109125