With lacquered wheels, the balance weights should be either 'stick ons' (stuck to the inside of the wheel) or clipped to the inside rim of the wheels. Clipping the weights to the outside rim will crack the lacquer and allow the ingress of moisture, causing corrosion. New Mercs always have the weights on the inside. Tyre fitters say that clipping to the outside rim gives a finer balance but I haven't noticed any difference at motorway speeds. With powder-coated wheels, it makes little difference but the wheel looks smarter and more like an MB wheel with the weights on the inside and out of sight.