What should foreigners be aware of when renting an apartment in Seoul?

Hello, I will be coming to Seoul as an exchange student this fall and am looking for an apartment with my partner. I found some decent options through sites like Enkostay and 33m2. There is one apartment that I particularly like, and I contacted the landlord. At first, everything seemed fine. However, when it came time to confirm the reservation, they said I needed to pay the full rent for the entire semester in advance. I can pay this amount, but it feels strange to pay it all at once. I'm also worried because I remember seeing a warning on Reddit last year about not signing contracts in advance. Is this situation common in Seoul? Is it risky to pay the full amount upfront? Additionally, if you have any advice or things to consider when renting an apartment, I would appreciate it.