1. At least in 1993, the official exchange rate was 6:1 but there were people standing outside the banks that would exchange it at 10:1. They were called the Yellow Cow Government.
2. They haven't been to China in a while, so they can't give an up-to-date black market rate. But a lot of economic indicators(property, bitcoin, etc.) show that people are willing to pay at least 20:1(conservatively).
3. Futures have to be traded in China. Otherwise they would absolutely buy large quantities of futures at the 7.44:1 price quoted here. There's political risk that the government might not enforce a futures contract if the currency gets too bad.
4. George Soros has already tried to pull a Soros on the Yuan, but it's harder when the government actively fights you.
5. At the current exchange rate, China is planning to print enough money to buy the US in a year, and the entire world in 2 years. So that exchange rate can't hold forever.
6. They reiterated that being labeled as a currency manipulator would be very bad for China, and there would be a huge surge in demand for the black market.
7. If you're caught smuggling USD into China, it's a pretty serious crime and they'll confiscate all of your USD. So the higher exchange rate has risk built into it.
8. You've been able to exchange $50k/person/year for a while, but they're starting to crack down on it. You need forms and approval for even $1000.
9. Since they're no longer in China, they wouldn't exchange at the 20:1 rate any more. But they'd happily bet against RNMB if you're selling futures at anywhere near 7.44:1 for December 2019. I'm planning to call a broker to ask about it, since I can't reconcile their pessimism with the fact that Yuan futures do seem at a glance to be traded on the Chicago Mercantile Exchange, which is a non-Chinese entity. Depending on what they say, you could probably earn a decent commission if you could refer a non-Chinese bank or something willing to deal with these guys.