Co-op City Hotel Seongsan vs The Best Jeju Seongsan: for 3–4 guests, count the third-person cost before the nightly rate

The framework is THIRD-PERSON COST CASCADE. Use headcount → legal room capacity → breakfast coverage → pool headcount → view → cancellation → final total. A three-person room does not guarantee that all three people receive every included benefit.

30-second decision

• 2 guests: third-person costs disappear; normalize room, view, breakfast and cancellation.
• 3 guests: Co-op's current Deluxe Twin uses Double + Single, but the source records free breakfast for two per room. At The Best, the summer rooftop pool is charged per registered guest during the paid season.
• 4 guests: The Best has a clearer public Family Double Twin / Family Suite route. Do not extrapolate Co-op's three-person Deluxe Twin into a four-person solution.
• Winter or no swimming: set The Best's pool line item to zero and compare the accommodation contract itself.

The third guest changes more than the room rate

At Co-op, the third-person risk is breakfast coverage

A room can legally sleep three while the attached breakfast entitlement covers only two. The source records breakfast around 07:00–10:00 with free breakfast for two per room in the relevant official information. If the third person will not eat at the hotel, that gap can be zero. Otherwise, add the uncovered breakfast cost before comparing totals.

For Co-op's room-view decision separately, see Co-op City Hotel Seongsan review.

At The Best, the third person can create a pool-cost multiplier

The Chinese source records The Best's 2026 rooftop-pool paid season from 26 June to 31 August, generally 13:00–21:00 with a maintenance break, at KRW 15,000 per adult and KRW 10,000 for children aged 36 months to 13 years, with under-36-months free. Those are source-bound 2026 figures and should be rechecked for your date.

If three travelers will actually swim, use three real age-based pool charges. If no one swims, the entire pool line should be zero rather than used to justify the hotel premium.

Four guests need a new occupancy search

The Best exposes clearer four-person Family products in the source. Co-op's Double + Single Deluxe Twin should not be stretched into a four-person booking. Once the party reaches four, re-enter the live inventory with all adult and child ages and compare only legal SKUs.

Compare exact-property totals only

Co-op City Hotel Seongsan

Booking.com — match headcount, bed, view and breakfast

Agoda — normalize third-person occupancy and breakfast

Trip.com — property 6578760

The Best Jeju Seongsan

Booking.com — match legal 3/4-person room and breakfast

Agoda — add any pool tickets you will actually use

Trip.com — property 6331474

Verdict

For two guests, both hotels return to a normal room-contract comparison. For three, Co-op's main hidden line is the possible third breakfast, while The Best's summer pool can create a per-person multiplier. For four, The Best has the clearer public family-room path; Co-op stays eligible only if a genuine four-person SKU exists for your dates. Count the entitlement cascade first, then compare prices.