Long before Karen, there was Nanni. (Geni/Wikimedia Commons) ****************************************************************** Almost 4,000 years ago, a Mesopotamian man named Nanni was so disappointed with the copper he bought from a trader named Ea-nāṣir, that he decided to write a formal complaint. Today, this Bronze Age clay tablet is the oldest customer complaint we know of – and it's a doozy. Writing and trade have an inseparable history. Some of the oldest surviving examples of written language are stocktakes and ledgers recorded in the ancient Mesopotamian cuneiform script. Since copper is a key ingredient in the very bronze the age was named for,...