We never use a taxi in Panama City. If you need a ride use Uber or Cabify. First - you will know the fare before you order your car. Second - their rates are always better then the rip-off rates charged by the taxis. Third - you can pay by credit card so you don't have to worry about the drive not have change (a taxi driver will always state they have no change, expecting you to just give them the change). Fourth - Uber and Cabify drivers are professionals... they are friendly and courteous (both traits are very unusual with taxi drivers) and their cars are always clean and in good condition (unlike taxis).
We had no problem using Uber while in Pamana City. Download the app before you arrive to save time. You can use the airport wifi to book a ride and you'll know the fare ahead of time. I think we paid $20-30 for a group of 5 from the airport to casco viejo.
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