In one of the lessons, it was mentioned that although tipping is not customary in China, to do so will be greatly appreciated. This may be true in tourist areas of Beijing and Shanghai, but this is very bad advice in 95% of China. I lived in Chongqing for four years and have spent a great deal of time in the traditional areas of China, and to give someone a tip is considered insulting.
When you give a tip to someone who has provided you a service, you are, in essence, saying..."You are poor and incapable of making a sufficient living to support your family, therefore I am giving you charity". My Chinese relatives and friends have told me this and I have seen it myself. Canadian friends visiting me in China have ignored my advice and offered a tip, and the reaction was anything but cordial.