On Gut FeelTrust it.
We arrived in Beijing Capital International Airport tired, sleepy, and four hours late. It was at least two hours until the first bus out to downtown. We just wanted to get to the hostel and sleep.
I followed my friend out of the airport to the taxi stand. The first cab guy showed us a card listing down the rates: 450 to 580 RMB for our destination. We said no. (We had already been informed by the hostel personnel that it would only cost around 130 RMB by meter.) As I was telling my friend that we should go back inside the airport and ask around, another guy approached us saying that his is a metered taxi. He put our bags into the trunk and we got in. Once in, I checked if there was a meter, but there was none. He was busy getting something on his left side, then turned to the right and connected that something to some wires. After some seconds of tinkering, he showed us his "meter." I had a bad feeling about it and wanted to get out of the taxi and get our bags from the trunk, but was stupidly too tired to persuade my friend. True enough, it was a scam. His "meter" ran up to more than 300 (and on the way, when we passed a toll booth, he said that toll is 80 RMB).
He did take us to our destination but stopped a few meters away from our hostel. It was a little after 4AM and the street was deserted. There was nothing else we could do, but pay up.
Lessons learn: Trust your gut feel. Walk away when you can. If you have failed to do so (like we had), learn from it, but don't let it ruin the rest of your day (and the rest of your vacation).
For more lessons from the road, please visit Go Learn.