I have done a number of transactions with a seller who will only accept cash. Since some of the transactions involve large amounts of money this can be challenging. I have always made it clear that if I were to send cash it would be at his risk. That said, I have never resorted to sending cash because even with risk allocation agreed to, I didn't want to have that tough experience. Consequently, payment is always challenging.
Ethics though... I agree with Kierkegaard that ethics are about the personal - we can only be ethical with respect to our own actions and decisions. However, unlike my transactions in paragraph one, these thoughts are veering off topic ;)
New York, New York USA