Not all clipping was illegal, or even nefarious. It was only a crime where there was a solid national currency system, which was far from universal. Many people would be trading in a variety of currencies, none of which was specifically backed by any laws forbidding clipping. Clipping would become so common that anyone with good coins was a fool not to clip them down to the local norm. There was also a general lack of small change in the ancient world. Heavily clipped coins, or even their clippings, likely substituted for the lack of smaller denominations. If a coin is worth its weight in silver, silver must be worth its weight in coins, clippings or not.