Buying and selling Bitcoin on a hardware wallet and not sending to an exchange

Both are quite easily done. Selling and buying bitcoin, straight from a hardware wallet, can be done at the so called 'fiatgateways' such as www.satos.nl (dutch), I believe Changelly deals with the same strategy. You simply open an sellorder and simply send the amount you have set to sell to the walletadres (straight from your ledger) given by the fiatgateway. Buying is exactly the same at these fiatgateways, not an exchange which comes in between your coins. Your keys, your coins! :)