[Mirioron]

>International trade has perfectly good mechanisms for dealing with this at present. See: Letters of Credit.

This works until you deal with a subject matter that (some) banks don't like or with people that (some) financial institutions don't like. It's entirely possible to be banned from Visa and MasterCard's services and this can sometimes mean that banks simply won't do business with you. Sometimes it's the subject matter you're dealing with that can be banned, eg certain types of (legal) porn.

>Probably still illegal to do business with you if the government has outlawed work with specific sanctioned countries, etc. Also, letters of credit.

He didn't say that the government has outlawed doing business with the country. He said that the government treats people from that country much more harshly. This would mean that businesses wouldn't want to do business with people from that country. Letters of credit don't work if the other country's banks aren't interested in dealing with businesses from your country.