This is also known as the FOP con (fresh off the plane). Any foreigner or tourist who has been in this city for more than 2 weeks is well aware of this old chesnut.
But as they say, a sucker is born every minute. A friend of mine got stung a month ago.
He called me as it was happening and I negotiated over the phone for a 1300 discount - or I would bao jing (bill was 1500, he spoke no chinese). They accepted. The 'sweet, young, culturally aware' girls are totally part of the con by the way.
Never order a cup of tea if you do not know its price ... lol