Overcharge for airport transportation

Sorry foreign buddies, I apologize you in behalf of Korea.
Some taxi drivers overcharge seriously to foreigners.
But they are now all arrested and I assume no more overcharge like that, since Korea government will keep keen eye on them.

Usually it costs around 40,000~60,000 KRW (regular taxi) and 70,000~100,000 KRW (balck premium taxi) depend upon your destination.
And you have to get receipt. If the driver don't give you the receipt then write down the car number and ask to the Korean police. You can trust Korea police. They are kind to foreigners.