This is always a problem with buying from overseas*, especially inexpensive items.
Ask if photographs of the problem would be acceptable. These can be attached to eBay Messages now.
You have three choices:
EBay will instruct the seller to send you a return shipping label, which is impossible**. When they do not, it is possible that eBay wll find in your favour and force a refund, without requiring the return.
Paypal will instruct you to return the item to the seller with Confirmation of Delivery. When the item shows as delivered, PP will force a refund. You will not get your return shipping cost back.
- Leave appropriate feedback and write off your financial loss.
When ordering from overseas, the true cost should also include the possibility of a dispute. The most effective FB is calm and factual. "Not as described, didn't work. Return postage more than cost of item."
*BTW-- a lot of those 'Australian' sellers are actually in China and ship from there. Again, especially inexpensive mass manufactured items.
** EBay does not understand that Return Shipping Labels cannot be used unless both are in the same country. He is in Australia and you are in Canada. Impossible.