Are utilities really included or do they bill you later?

For goshiwon, 공과금 포함 is genuinely all-in and there is normally no later bill. This is one of the real differences from every other Korean rental.

Why it works that way: the building is metered as one unit, not per room. There is no individual meter on your room, so there is nothing to bill you for afterwards. The operator absorbs the variation across all the rooms and prices it in.

The narrow exceptions worth asking about:

1. Aircon in some older buildings is coin or card operated in summer, so cooling is effectively pay-per-use. Uncommon now, but ask specifically: "에어컨 따로 돈 내요?"
2. A few buildings put a cap on very heavy use and will speak to you if you run a heater 24 hours a day with the window open. This is a conversation, not a bill.
3. Laundry is sometimes 1,000 to 2,000 won a load rather than free.

On winter heating specifically, since that is your worry: goshiwon rooms usually have either central heating on a building schedule or a small individual unit. Either way it is included. What people actually complain about in winter is not a surprise bill — it is that the central heating runs on the building's schedule rather than yours, and some buildings keep it modest.

The two questions that close this off completely when you view: "관리비 따로 있어요?" and "에어컨 따로 돈 내요?" If both answers are no, the advertised price is the price you will pay every month.

And get the answer in a KakaoTalk message rather than only in conversation. There is usually no written contract, so that message is your record.