Returned item- is this normal for the store to do this?

If I purchased an item online at a discount, returned it in store. But changed my mind and want the item back. The cashier charged me full price without the discount and gave me the same opened item back. Is this normal? If they’re going to charge full price shouldn’t they give a new box? Plus they kept the receipt of my original purchase. (I did use the item a lil bit to test if I like it)