Regular Taxi in Seoul

There are two kinds of taxi in Seoul. Premium and regular. Premium costs one and half more than the regular taxi. Premium taxi is dark black color.

Seoul is notorious for its heavy traffic jam. Taxi may not bring you as fast as you anticipate. Because of the heavy traffic, taxi price is also not very accurate. But generally speaking, you may not pay more than $25 to move in Seoul.

Here is some price example, assuming the normal traffic.
From GangNam to Sinchon : $15
From Seoul Rail Station to GyungBukKung : $4
From Express Bus terminal to GangNam : $7
From Inchon Airport to Seoul city area : $60

Most taxi driver is kind and honest and may not cheat foreigners. But some taxi driver may not know the shortcut (Remember, Seoul is huge huge city with 12 million people) They may expect some tip from foreigner. (Local Korean does not tip or sometimes give the change)

Taxi drivers barely speak English, but you can ask for telephone translator.
Or you can ask for writing your destination in Korean letter and hand over the paper to the driver.