Many classical books have a fahrasa (appendix listing teachers). Reputable modern editions include a “Certification of Authentication” signed by a committee.

He showed Layla an example: a book titled Al-Ghazali's Mishkat al-Anwar . "There are two versions. One is authenticated by Ghazali's own student, Abu Hafs Umar al-Suhrawardi. Another version contains additions from later Sufi mystics. A verified edition will tell you in the introduction: 'This manuscript was compared against the original in Ghazali's own hand, held in the library of Damascus.' Without that note, it's just ink on paper."