bazz61 said..
if you you use a hidden IP address would you still be charged GST or is it identified by where the postage is ..?

You can never hide an IP address, its either going to show up as your real one in Aus, or one somewhere else.

Either way, if your delivery address in in Aus, I suspect that it will decide to charge GST, as you have suggested.

I haven't bought anything from ebay.com , and pretty much use the .au site, so I don't know if it pushes you from one to the other. I suspect it is smart enough to do that, as its relatively trivial to do. Using Paypal, or your delivery address, it should be easy to identify an Aussie customer.