Should I enter the delivery/pickup and installation/restock fees as positive or negative on a return?  

When entering amounts in the Delivery/Pickup and Installation/Restock fields in Enter a Return, you have the option to charge or refund the fees. Positive amounts entered in these fields on the Payment page of the return are added to the refund amount, thus increasing the amount due to the customer. Negative amounts are subtracted from the refund amount, thus reducing the refund due to the customer.