The short answer
Ask for the meter before you get in a petit taxi, the small beige cars, or agree the full fare out loud before the car moves. If a driver says the meter is broken or quotes a high flat price, wait for the next one; there are plenty. For the airport, a pre-booked transfer with the price fixed in writing removes the negotiation entirely.
In more detail
The word to use is 'compteur', the meter. Most petits taxis are metered, and the friction comes when a driver claims it does not work or offers a tourist price instead. Drivers waiting at the square and outside the station are the most likely to try it. Walking a block away from Jemaa el-Fna before you flag a car usually gets a fairer start.
Know where you are going before you get in. Most riads sit on lanes no car can reach, so taxis drop you at the nearest gate or square. Save that landmark on your phone, along with your riad's location, so you can tell the driver exactly where to stop.
Arrival is when people are most tired and most likely to accept a bad deal. That is why many visitors book their airport pickup before they fly. The driver waits in arrivals with your name, and where the lanes get too narrow, someone walks you and your bags to the riad door.
Good to know
- Have a rough idea of the fare before you ask, so a high quote is obvious.
- Carry small notes; drivers often claim to have no change.
- After dark, an arranged car back to your riad's gate is easier than a taxi rank.