What sort of remedy?
Consumer Rights states that, if it is possible to have the item repaired to your customer's satisfaction, and then you should be given the opportunity to do that, providing the time to do it is not excessive.
If it can't be repaired, or if it needed more repair, then you should offer a replacement, if this is not possible then a full refund should be offered. In such instances, you can offer a credit note.
The goods do not have to be returned with the original packaging, but your customer must be able to show proof of purchase, such as a receipt. Price tags and credit card statements are not necessarily considered proof of purchase.
Your customers have no legal right to a remedy if they have simply changed their mind, or the item is an unwanted gift, or the wrong size etc. However, under such circumstances, if the salesperson agreed at the point of sale to give a refund if the item proved not suitable, this may become a 'condition of sale' and they may insist on a refund.
Some stores have a very flexible and customer-friendly policy of exchanging goods. They do this for good will, not because Federal law requires them to.