If there is any major fault (e.g. the usb is not working) return the products and receive a 1) replacement or 2) a full refund (excluding any postage charges) for your purchase.
Simply email email@example.com and tell me what the issue is, then return the products to me and when I receive the products I will replace or refund the full purchase price (unless its damaged)
Products damaged by you cannot be returned.
You cannot receive a refund simply because you changed your mind.