Can you trust the black market and money changer in front of and inside the bank of china? even the cash the money out of the machine with their bank card? U still dunno their IDs.

some Fake money in between?

Don't trust them.

Asking for trouble. As above, don't trust.

Most of those people make their real money from arbitrage, rather than slipping counterfeits, though it's always best to be safe. If you don't have a trusted dealer (ie recommended by friends or whatnot), then the only way to be sure is to have them deposit the money directly to your account, which some of them will be willing to do.

Xiefei's point: yes.