The Amazon link is present on every item and doesn’t mean you have to buy the title. It is also used as a temporary link to alert the Library to purchase the book. If the level of importance of a reading list item is “suggested for student purchase” you may want to consider purchasing a copy (although the library will have a limited number of copies).
The Amazon link does not mean that the library endorses this book supplier over any other but it does give you the opportunity to price check a particular item.