Rejecting girls should not get you into trouble, as it is common for HGs and walkups to get rejected. Part of the business.
As I don't speak much Chinese, I just shake my head and say "Not OK", no thank you. Maybe motion towards the door that I'll be leaving.
Here's one report of troubles with a walkup who wanted to be paid $100 when punter stepped inside the room, but rejected her services:
http://forum.sex141.com/eforum/viewthread.php?tid=27884