Australia online marketplace purchase: who is responsible if the item never arrives?

Responsibility can depend on whether you bought from the platform itself or a third-party seller, and on the platform terms and Australian Consumer Law. Keep the listing, seller details, order confirmation, payment proof, delivery tracking and platform messages. If the seller does not resolve it, use the marketplace dispute process and consider payment-provider remedies where available. Guide: https://getinstantlaw.com/online-marketplace-purchases