They have their way of getting the discount back from you, also a very special way of determining REFUND.

Just to share my recent experience.
Bought item A rm160 with coupon (it is overprice but slightly cheaper than the market price after discount), and item B rm30 with coupon. Paid in a single transaction. Item B is different from what the merchant had advertised. They agreed to refund and told me no need to send the item back to them.

Guess what happened. They refunded me rm4. How come? RM 30 - discount for item B - discount for item A. And this is the final decision from the higher authority.

Lesson learned: perform transaction for every single purchase.