Taxis are notoriously criminal and I love to say it. They're a caste, generally rightwing, highly abusive. They of course rip off tourists as a way of life. Prices should be posted in the cab in plain view in English, French, etc. Insist that they immediately turn on the meter when you get in a taxi and only pay what's on the meter. The rest is bullshit unless you're going to the airport. Those prices should also be in plain view.
Any car without identification numbers and meters is not a cab. Don't use them. Hell, I wouldn't even take a cab for that matter.