I am a regular visitor to China and would not have tried the $10 trick, In PEK they don't play that way.

Had they refused, nothing would have happened except they would have been stuck in the airport for anything from an hour to a day to get it straightened out (especially if you got the Embassy involved). Someone I know had a similar situation into Brazil a few years ago, he hadn't had a visa and no one checked in Miami. They flew him back and forth for FREE in order to avoid the fine. AC screwed these people, plain and simple. The above poster gives the advice. Call Visa and dispute the charge immediately, that is probably your only chance.