Rental Ethics

I recently rented a textbook from Amazon.com. I only needed the textbook for 4 weeks and I am now ready to return it. When I went on the website I saw that I can actually return the textbook for a complete refund because I am not keeping it until the end of the rental period allotted. However, I did use the textbook for a few weeks already...Should I wait until the refund period has ended so that I don't get a refund since technically I gained from using the textbook? Or is it ok for me to get a refund? Thanks

I would imagine that Amazon is perfectly aware of the fact that if you rented the textbook and are returning it before the end of the rental period that you might have used it and don't need it any more. That would seem to indicate that you can send it back early and receive the refund. However, perhaps it would be correct to send a message with the book saying that you used it and asking them whether it is acceptable to ask for the refund or not.