Amazon charges you for return shipping (or obliges you to use your own shipping, e.g. USPS) depending on the reason you are returning an item. If you are returning it just because you decided you didn't want it, they don't pay to take it back.
That was my experience with some housewares stuff, about three weeks ago. I decided to take the item down to the Post Office to ship it back rather than using Amazon's label, because it was cheaper that way. (If I'd used the label, they would have deducted $8 or something out of the amount they were going to refund me eventually; USPS was something like $4-5.)
