My advice, dispute it. You should win with picture evidence. When it comes to posting it back, get a box get some bricks that come to the correct weight and post that to him. Will be signed for, and what proof does he have he never got it back? You got a postage receipt with proof of postage and has been signed for. Harsh, but I done it to some fuck wit that screwed me on a honda engine. I sent it back on a pallet with paving slabs. Rebuilt the engine at a garage and the refund paid for it!