If you earned stamps on a purchase, returning items from the purchase may cause you to lose stamps, depending on the value of the return.
Example: You earned 3 stamps for a purchase of $31. After returning a $10 item, your revised purchase total would be $21, meaning 1 stamp would be deducted from your stamp balance.
Rewards are applied across the items in your purchase. If an item is returned, the rewards applied to that item will be returned to your rewards balance.