How to manage costed items when they come back for repair?

Hi All,

Scenario: we manufactured ItemA and shipped to the customer; it costed us 500 dollars to manufacture (average costing).

Then customer shipped back the ItemA for repair and we received in a Non-Asset sub so there's no impact on costing. We also create a project for each repair to track the costs and create a project cost group as well.

I would like to hear from you how you manage repair without impacting costing? Do you follow the same approach of non-asset sub/Project cost group OR just non-asset sub? What other controls do you put in place in INV, PA, WMS etc so all the repairs stay in a non-asset sub and don't affect costing.