구매했던

In a sentence

• 제가 구매했던 책을 친구에게 빌려줬어요.

  I lent the book I had purchased to a friend.

  The term '구매했던' is used here to describe an item ('책' - book) that the speaker purchased in the past.

• 그가 구매했던 가방은 정말 멋져 보였어요.

  The bag he had purchased looked really stylish.

  In this sentence, '구매했던' modifies '가방' - bag, indicating it was bought by '그' (he).

• 우리가 구매했던 자동차는 이제 너무 오래되었어요.

  The car we had purchased is now too old.

  Here, '구매했던' relates to '자동차' - car, indicating a past purchase made by '우리가' (we).