Australia online marketplace purchase: do consumer guarantees still apply?

Yes, if you bought from a business seller. ACCC says the usual consumer guarantees apply to online purchases just as they do in physical stores. On marketplaces, those rights generally apply against the seller you bought from, not automatically the platform. Private sellers are different and most consumer guarantees do not apply. Official source: ACCC. Guide: https://getinstantlaw.com/online-marketplace-purchases