How would you convert bitcoin to USD? You need a buyer. If you go through an exchange, you have to prove your identity to the exchange. If you go through an individual, there's a risk of not receiving your money if you make the transaction online, and if you do it in person, you risk your identity again.
There's no guarantee for either party that the transaction will be completed successfully. Either party can take the money and run. So you risk your money or your identity either way.
You can do things like deposit a physical incarnation of the stuff somewhere, or several locations, locked in a series of locks, and exchange geo coordinates and keys in a series of trades
There's no guarantee for either party that the transaction will be completed successfully. Either party can take the money and run. So you risk your money or your identity either way.