I actually found a link earlier with instructions when I was looking for something else.

http://pages.ebay.com.au/help/sell/buyer-requirements.html

When you get in there:

Set the unpaid strikes to 2 in 12 months

Tick to block buyers from locations you don't post to

Set buyers with policy violations to 4 in 6 months

Don't worry about the negative feedback score because buyers can't be left negative feedback any more.

The next option is your choice whether you want to activate that one or not.

Tick don't allow blocked buyers to contact me (else they contact you asking to lift your blocks!)

Tick apply to current and future listings.

Submit.

These settings will give you the maximum protection (in my opinion).

When you're done, go back to site preferences, click show on postage preferences, then scroll to exclude postage locations, the click edit. It's in there where you can block overseas bidders if you just want to sell to Australian buyers. If you don't want to offer international, tick all the boxes. 

If you reopen the buyer requirements section, you should see a link saying Buyer Requirements Activity Log. Clicking on that will show how many people have tried to buy your items AFTER you put the blocks in place. When you see them stack up, a huge sigh of relief is in order!!

Good luck!