Q. I purchased an Mp3 player. Later I saw the same thing cheaper online. I bought the cheaper one and used the receipt for the older one to do the refund. We are debating if this was correct?

A. You have deceived the companies. You can only return the item to the place you had purchased it from. Should you inform the company of what you are attempting to do, and they accept the online product in exchange of the one you physically purchased from them, this would not constitute deception and would thus be allowed.

The transaction as you have described would not be allowed.

Allah Certainly Knows Best.