So just having a look at how eBay AU is handling the GST.
If I search an item, items that are coming from overseas are being shown with pre-GST prices in the search results and item listing, and it's not until it's in the cart that I can see GST is added.
For one thing, makes it hard to compare results when some items (from AU sellers) will be the price shown and others will end up being 10% more.
Legally speaking though, I guess that might be how they do it in the US, but in AU all retail prices must be displayed GST inclusive right?
Ebay's issue is there's no guarantee that you will be having the items shipped to your Australian address. You could be having the item shipped to a US address.
I guess they could do it like Amazon UK and simply deduct the GST portion in those instances.