Couriers re-weigh and re-measure parcels at their hubs. If the re-measured chargeable weight exceeds the declared weight, a discrepancy charge is raised against the seller — often days after the shipment moved, which makes it easy to miss without automated tracking.
Always keep a weighing photo and dimension proof at packing. Most weight-discrepancy disputes are won or lost on whether the seller can produce a clear image of the parcel on a scale with its label visible.