Buyers can't initiate an eBay cancellation request.

This is changing though as part of the latest updates on ebay.com and hopefully will change on AU soon.

We’re also streamlining the cancellation process to make it easier for buyers and sellers to cancel a transaction directly from My eBay. Buyers can request a cancellation if they change their mind within an hour after the sale (as long as you haven’t already shipped the item). This will help reduce the hassle of unpaid items and help you get your merchandise back up for sale faster. Sellers will also have the option to cancel transactions directly from My eBay instead of the Resolution Center and, if the buyer paid with PayPal, sellers will no longer need to wait for a response from the buyer.

http://pages.ebay.com/sellerinformation/news/fallupdate2014/after-sale-experience-details.html