When you create a threshold discount (for example buy $100 get $10 off) the discount amount is pro-rated to the lines in the transaction. If I was buying an item that was $90 (Line A) and an item that was $20 (Line B) then the result is that I have a $10 discount for a total of $100 (ignoring taxes here). The $90 line will have a $8.18 prorated discount and the $20 line will have a $1.82 prorated discount. This is fine in the context of a sale but if I then return either item, I will invalidate the original threshold for the discount of a $100 or more purchase. In this case the POS currently refunds exactly what the customer paid, so $81.82 if I refund line A and $18.18 if I return line B. This way, a customer could return one of the products, and still benefit from the discount on the other one, even though they technically shouldn't have gotten the threshold discount after the fact. The refund should be the net amount paid for the item return, less the discount applied on the other item. For example, if I return item B, then I should give $18.18 - $8.18 (discount on item A) for a total refund of $10. If i returned item A, then the refund would be $81.82 - $1.82 = $80.00. The one caveat is that this could be confusing to the customer, however, it would be a deterrent to try and game the system.