As posted by Dealking (https://www.ozbargain.com.au/node/497950), 20% off is back at the Sony Australia store. This means that OzBargain favourite headphones WH-1000XM3 are available for $319.20. These are seconds, listed as refurbished, but still come with a 12 month Sony warranty.
Edit: My bad, got the date wrong on this.
Today only there is 12% cashback on eBay through Cashrewards - stacking this onto the deal makes the headphones $280.90, which I think is the cheapest they have been in a while, and probably makes it worth purchasing refurb/seconds stock.