Don’t buy your textbooks until you’ve confirmed with your instructor that they are required.
You can do this by emailing the instructor, contacting the instructor’s department, or waiting for the first day of class when you meet the instructor. If the syllabus is posted online, check that to make sure the books listed at the bookstore are the same as what the instructor wants to use.
Book order paperwork (at least here it is on paper) goes through many hands, and they are usually written by hand, so mistakes can and will happen. Also, when there are many sections of the same course, some instructors may decide to add or remove supplemental materials.