Ensure the book you are buying is the correct edition. If unsure, ask your instructor.
Check to see if the book includes an access code for online content. If your instructor says the code is needed, and your code had been used or is expired, you'll be stuck buying a new code, which can be more costly than buying a new textbook.
Buy Older Editions
Sometimes you can find older editions of textbooks available for sale online.
Before Buying an Older Edition: Check with your instructor. The content can occasionally change between editions, and you might be missing out on important content!
Rent your Textbook
The following sites offer rental options for many popular textbooks: