Flag items in the product master as "Returnable". Then when a returnable part is used on a work order the system would create return line on the WO. Consider an inventory transfer record to require the tech to return these type of parts to a returns warehouse, I have seen this done very well in Dynamics GP by creating a good warehouse and a bad warehouse for the tech. Returnable parts are put in the bad warehouse for trackability. Typically Returnable parts have a core charge or value, these type of parts are typically high value and can go thru some type of refurb process or be returned to a vendor at a price or exchange value.