It enrages me how many times I hear about people (mostly tourists) getting ripped off by taxis.
If you are taking a taxi, to almost anywhere (as long as it stays inside the city boundaries) It should cost around 4 dollars on average, 5 or 6 dollars if you are travelling with a lot of people or it is farther away than normal (you will be able to tell if you see long high way like roads, for example going to albrook mall). One time I even heard of someone who got charged 100 dollars for a fare from Radisson Decapolis to the historical center of the city, which should not go over 4 or 5 dollars.
A ride from the airport, to almost anywhere in the city should cost around 30-40 dollars.
PS there have been several assaults made to taxi passengers lately. To stay safe, specially at night, try to call cab service.
--Sorry for any grammar or spelling mistakes I made, I tried to make this quick.--