On 15 Teves a תשובה was posted that allowed returning an item to a Jewish store for a full refund even though the item was used. The סברא given was because it was yours when you used it. Why is this different than שו”ע יו”ד סי’ קעד סעי’ ז that the Mechaber rules that if a sale is canceled than it is ribis unless you pay for the usage. Also see סעי’ א there regarding a seller who wants the item back when he has more money. Even though the פתחי תשובה (in S”K 1) bring opinions that hold that it is permitted if you are going to sell the item back not just cancelling the sale, why are you assuming that this is the understanding in a regular return policy? Furthermore, if we assume that the store is buying back your item, not just canceling the sale (as your תשובה says), why is the store returning the full amount, it should pay a little less since the item is worth a little less after your usage? Thanks.