If you wait at the official stand in PEK airport, tell the driver "天安门广场" I would REALLY be surprised if you had to pay anything above meter rate.

I'm not saying that all taxi drivers in China are honest - but at an official location like PEK, they're sh*t scared to even try a scam. If you try to outsmart them, by going to the road and getting a "cheaper ride", then it might be very well that you end up in a "private" taxi, which will cost you more in the end..

There are scams in China - that's for sure - and some people apparently get more attention than others by the scammers (I've never had any scam "attack" on myself so far, and I'm quite often in China) - but the case you're describing is just not really happening. So yeah, you must have done something the regular traveller would usually NOT do - otherwise I'm sure FT would be full of posters, especially this thread, to report about "how I got scammed by taking a taxi from PEK airport to 天安门广场...