You’d just pair it with your Steam account just like you do with phones to your carrier. The transaction in this case would require releasing the Deck from the current owner before buying (which could be verified easily, perhaps with a serial or something).

I guess you could do it with an NFT, but just involving Steam in the transaction (registering a new account) would absolutely work.

That said, I don’t want that because that would just turn stolen Decks into ewaste. I’d rather my stuff get used than tossed in a landfill.