Tipping isn't common in China. In fact, I don't think I've ever tipped in China. That's not to say I'm extremely stingy and/or hyper-critical of waitstaff. It's actually because in China, tipping can be considered rude. Meanwhile, in the US, workers in the service industry are often reliant on tips to make a living. Having become accustomed to not tipping, it's definitely hard to not want to scream at restaurant owners... "Just pay your staff a fair wage!"