They might have one or several copies, though maybe not the right edition and never enough for an entire cohort of students.
At my university, students who didn't buy the book would simply make photocopies from the library's copy or from a friend's. But then the photocopiers were modified so that they only operated using credits from "copy card" that was tied to the student ID.
I never knew anyone who got into trouble, but heard that you'd be called in if you were making "too many" copies.
edit: an extra word