If you are traveling to China on a Group Tour you will more than likely come up against this situation.  Tour operators will advise that tipping for good service is now common practice in China for Local Guides and Drivers. Some will have a fix amount to be paid on arrival (prefered) as you know and agree to the amout you are paying. The other approach is to suggest an amount (say $10 Guide $5 Driver per day) which sounds reasonable if it is a small group.  What is more likely to happen is the group will be 35 -45, a National Guide will arrive whose main function seems to be collecting the "tips" indicating that the Local Guide and Driver are not paid and the "tips" are for that purpose.  This National guide may also demand a tip of $10 per day for themselves.You may be required to enter your name and the amount you "tip" on a list which can be intimidating and raise concerns of the possibility of retribution for non compliance.

Consider this, if you are in a group of 35 on a 10 day tour, and all pay the suggested amount ($250each) the collection would be $8750. Where as reasonable renumeration and a 10% tip would not exceed $900. This is a surcharge and if traveller views it this way and are happy to pay, all well and good. If you go believing this is truly discretionary "tipping" it may impact   negatively on your experience.  

While pure "shopping stops" are banned whereby the merchant rewards the tour operator with hefty 40-50% commission payments for stopping at a certain isolated store, reports have emerged already on ways this will ban will be worked around.  Be very skeptical of any store recommendation made by the tour or guides.  Chances are there is some money changing hands in return for the endorsement.  Always shop around among stores, and then bargain where you find the beginning prices more to your liking.    

The guides and drivers have a lot of ways they skin the tourist.  Do not feel sorry for them when they say they depend on tips.