Books were scarce in the pre-modern era, and so librarians needed something more potent than a library fine to punish people who lost or destroyed books. What did they resort to? Many important books included curses that would befall people who lost or destroyed the book.
There is little evidence regarding how effective this was compared to the modern day solution of library fines. One problem with this approach may have been that many people who might have stolen or destroyed the books were either entirely illiterate, or did not understand the literary languages (often Greek and Latin) in which the books were written.