It can be simpler than that even without banks. My own Chinese family “launders” money using similar mirror transactions, but a bit simpler. They often have cash coming from US restaurants and rentals, and they want to send that cash to their family in China, sometimes to invest into Chinese businesses. So first they find a Chinese person in Los Angeles (let’s call him Mr X Lee) who wants to receive cash from his family in China (let’s call them Lee family). My family gives Mr X the cash, at the same time asking his Lee family in China to give the same amount of cash to my relatives in China.