You don’t need to use taxi in İstanbul. But if you have to use it, you should be careful. Because some taxi drivers have many tricks like everywhere in the world. The cars which are working as taxi, have always Taxi Meters which start from 2,50 Lira and 2 lira for every kilometer.
Some drivers will say you don`t need to ask questions such as how much does it cost to go Taksim or Sultanahmet area! Because they will not say taxi meter price, they will say that it costs you 40, 50 or 60 Lira and they will not open taxi meter. If they open taxi meter, it will cost you 20 Lira.
When you get on a taxi, you should make sure that driver opened the taxi meter. If not, tell him to open it or get off from taxi. Because they behave as if they forget to open taxi meter and ask you more money when you get off. In case you have problem with them, you should take the number of taxi and gave it to police. There is a big punishment for these kind of tricks.
If they open the taxi meter, you can use it. If not, you can find somebody else who will open taxi meter for you. You should always check taxi meter and pay money in Turkish currency not in EURO or DOLLAR.