紹介者가 좋은 冊이라고 해요.
What is the difference between 라고 and 다고? I wrote 다고 and got wrong but is it correct?
Declarative verbs use ~다고 with the exception of the verb "이다" which uses the form ~이라고. So, "다고" is incorrect in this case, unless you said "책이 좋다고"