When to use customer in Korean
Korean: 손님[ son-nim ]

When to use it
손님 means a customer or a guest. You can use it for a person who comes to buy something, and also for someone who visits your home. It is a polite and common everyday word.
Example sentences
집에 손님이 왔어요.
A guest came to our house.
오늘 가게에 손님이 많아요.
There are many customers in the store today.
손님, 이쪽으로 오세요.
Customer, please come this way.
엄마가 손님에게 차를 드렸어요.
Mom gave tea to the guest.
학교에 손님이 오셨어요.
A guest came to the school.
호텔에 손님이 늦게 도착했어요.
A guest arrived late at the hotel.