Buy backs work in the same way as your semester-end buy back at your campus bookstore. Merchants are standing by, ready to give you cold hard cash for your textbooks. Keep in mind that textbook prices fluctuate throughout the year. In the beginning of a semester, you will get the most money for your buy backs (they need more textbooks to sell!), and at the end of the semester you will get the least (everyone is selling theirs back, as well). You can often get a significantly higher offer by waiting for the following semester to begin to sell your textbooks back.
Once the buy back merchant has received and processes your textbook, you will receive the money for it. It's that simple!
You can! Often times you will make more money by doing just that. However, keep in mind that Amazon will take a healthy chunk out of the sale of your book. Not to mention you will have to wait for a buyer to come along. Buy Backs are immediate.