We often charge a design fee and then refund the fee if the customer makes a purchase.  How can we handle this?

This situation can be handled by creating a non-inventory product (for example, called Design Fee) in Advanced Product Settings and assigning it a replacement cost of zero, along with a selling price equal to the design fee.

You can then add the product to the order and later delete it if you no longer want to charge the fee to the customer.

 When creating a non-inventory product, you must assign it to a non-inventory product group.  Thus, you may need to create a non-inventory product category and a non-inventory group associated with that category if they don’t already exist in your system.