The Chinese mob (wink wink) has the biggest money laundering operation in the world. They have brokers who pick up (source) and deliver (destination) the cash. They do all the currency conversion. And then have an internal market to auction the conversions. All over Chinese government controlled networks like WeChat. Very clever.
The Triads have been doing this kind of dark market money transfers for decades (it's mentioned in the book Mr Nice like it was old news in the 80s). I've met Chinese people who use it to send/receive from family and investors in mainland China. I've met agents who investigate the networks of companies Chinese mobsters make to cover up their tracks.
Financial Times doc https://www.youtube.com/watch?v=EjGIp7kdS6E#t=8m32