Charge Restocking vs. SAFE-T

Customer returned a used item (bought new item from us) with a serial number not matching the packaging (we track all shipments by serial and have photo evidence at shipment). Do you charge a full restocking fee, then file claim with Amazon, or just refund customer 100% of cost, then file SAFE-T? This is FBM not FBA. Thanks for anyone with experience on this for replying. Item cost was $600.