i had the same experience ar. On the 1 of july this year a best friend of mine and I arrived at Lo Wu and planned to take a bus. Some jerk came over and said it was already too late la no bus la. Then he took us to take a taxi. When the taxi arrived he said we have to pay first. My friend gave him 200 RMB and then he said one of those 100 RMB note is fake. We were sure the money was not fake because my friend only change 500 in the exchange shop in HK and we had already checked the money. Anyway we did not argue with him and instead I took the other 100 RMB note from him and gave him all the small notes I had in my pocket (some 5 dollars, 1 dollars, 10 dollars). This way he could not trick us anymore.
Please be careful at Lo Wu because these jerks know how to change your money very fast. Lo Wu is full of taxi lining up in the taxi stop so, brothers, please do not even respond to any person who ask you whether you want a taxi. These days they do not care to earn a commission by offering you a taxi without you waiting in the line, they just want to change your money! And they do it by first taking you to a place where there are not too many people and say something like "the taxi is over there and we have to go there the taxi is waiting bla bla bla..." and once you are there they will change your money. So, brothers, be careful!