Being in China, you have to haggle. It can be quite fun, trying to get a good deal, especially when the stakes are low. Haggling is necessary since prices are not posted, so there is no point of comparison, and search costs are high. The first Mandarin I picked up were numbers to help in my bargaining. A student recently asked what the point of learning the numbers was if you can simply tap on a calculator your respective offers. My global answer, not just restricted to China, is twofold. First, responding in the local language signals that you are at least knowledgeable of some words, might have spent some time in the country, and that you are putting forth an effort. The second reason, however, is that when native speakers ask for the price of an item, the response is aural, not on a calculator. I then get more information without engaging with the seller. I still probably do not pay the local price, but at least I do better than the bus full of German tourists.
