It is not clear to me from the article and from the brief googling I did, how they came to the conclusion that there was no trading class? What evidence did the

It is not clear to me from the article and from the brief googling I did, how they came to the conclusion that there was no trading class? What evidence did they use to prove this absence? It seems to me the ruling class of any society works by trading with each other, in promises if not in currency. I don't see how it could work any other way?