This is the 2357th most frequent Korean word.
고객이
"Customer" or "client."
In this sentence, "고객이" is the subject indicating who performs the action of satisfaction.
고객이 만족하시면 저희도 기쁩니다.
If the customers are satisfied, we are happy too.
Here, "고객이" identifies the customer performing the action of leaving a review.
고객이 가게를 떠나기 전에 리뷰를 남겨주셨습니다.
The customer left a review before leaving the store.
In this case, "고객이" specifies the customer who executed the inquiry related to the product.