Estate agents are called “Budongsan Junggaesa” in Korean and can be found all over Seoul. Their role is primarily to mediate between property owners and the purchaser.
Some agents specialise in working with foreign clients, others have little or no experience in this area. Clearly buying a house can be a complex business and getting all the answers and clarifications you may need may be hard if dealing with the latter.
As you would expect estate agents work on a commission basis. The commission is paid by both the buyer and the seller and is normally equivalent to about 1% of the purchase price of the property. The lease is generally signed between the property owner and the buyer, a process which is overseen by the estate agent.
To avoid misunderstandings caused by language or other make sure everything is down in writing. Don’t take anything for granted: always ask until you get a satisfactory response to your questions!