To initiate a return, you must inform us of your decision within the Cancellation Period by contacting Arduino customer support and clearly stating your desire to return the Product.
Arduino customer service will provide you with a written return authorization (‘RMA’) that must be included with your return shipment to Arduino so that Arduino can identify your shipment and with a return address. The customer shall arrange to have the return shipped back to Arduino.
The conditions for accepted returns are:
Arduino will accept returns on a very limited basis. Arduino accepts returns only within thirty (30) calendar days from the date of Customer’s receipt of merchandise. The customer shall arrange to have the return shipped back to Arduino. Products must be received by Arduino in a “resalable condition”. “Resalable condition” means the Product has no signs of: use, wear and tear, cosmetic damage, or any other damage.
You can review the full document here.