The meter is not optional. If a driver says the meter is broken, get out. From IST, use the airport taxi desk or a ride app. From Sultanahmet to Taksim at night, agree on nothing except the meter. Keep small bills. If someone 'helps' with your bag at the curb, they will want a fee you did not ask for.
Istanbul taxi scams
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LO local 1 -
AD admin 2 BiTaksi and Uber still work in most of the city. The yellow taxi is fine if the meter is on. Airport desk taxis are the least drama after a long flight.