can i resell an item bought by an australian buyer

Kia Ora Anne,

You must first ascertain whether your Buyer has an NZ address the parcel can be sent to, if not you can let them know you don't Post to Aus. & that where there is No Australia option provided in the shipping options or Listing details itself they need to ask the Seller in the Q&A section prior to purchase. - Refund any payment they may have made & apply for a refund of your success fee, then Yes! you can make a Fixed Price Offer to other Members.

You may like to add to your Listings that you don't ship to Australia. - Cheers.

Or just send it to Aussie. If you have access to a printer is all very easy. You can book a courier online directly from NZPost. I send 3 or 4 week like this all over the world. 

You can get a quote first to ascertain the costs, and pass this on to your buyer. 

https://www.nzpost.co.nz/tools/rate-finder/sending-internationally/parcels