The tea-house scam is probably the most prevalent, where innocent-looking 'students' approach foreigners in big tourist areas (like Tiananmen Square or The Bund) and invite you to go tea-tasting, then rip you off with a massive bill and similarly massive guys blocking the door.

Taxis are known to overcharge, epsecially from the airport. Just make sure you either agree on a reasonable price beforehand, or insist on using the meter. If they claim it's broken, find another taxi. And there are heaps of websites out there that can indicate what a 'reasonable' price from the airport to the centre of town should be.

Another one is the hospital scam. Particularly at smaller hospitals, after you've been treated they will present you with a bill for all sorts of rubbish like bedding and drugs you either did not use or don't exist.

Best thing to do is have a Chinese friend you can call on if you sense that you're being ripped off.