Nearly nothing can be bought nor sold via BTC without fiat transfers.
That's false, BTC is a currecy and can be used as a form of payment through merchants that accept payment in BTC, and there are so many of them. You don't need fiat transfer to send BTC from your BTC wallet to a merchant who accepts it or by scanning their QR code for payment, once sent, the merchant would release the commodity to you, just like every normal payment method.