Not all taxis are created equal.
Many foreigners learn this the hard way, which means paying anywhere from USD $5 to $10 more than the going rate for a taxi.
The first place you will get hit with the “special” taxi rate is outside the airport. The most convenient taxis, the ones parked right there, tend to charge more 
than if you arranged your taxi in advance with someone like Carlos Aleman.
The airport is to be expected, for sure, but the raised prices go beyond Tocumen to the streets of Panama. Two of the most common places you will pay extra are outside hotels, and outside malls, such as Multicentro.
To avoid paying extra, walk across the street and hail down a taxi. If you are going to be needing a lot of transportation, you can get a driver, or just get the number of the first taxi driver you find that you really like. Then, you can call him for advance pick-up.
Make sure that you always get a price quote before you get in the taxi to avoid confusion. These aren’t metered cabs like the kind in New York, and you can end up paying a lot more than you were expecting at the end of a trip.
Great article. How much is the normal price to downtown?