You signed a five-year supply agreement with a Bronx manufacturer worth $6 million. Buried on page 14 is a clause saying no changes are effective unless in writing and signed by both parties. Eighteen months in, your operations manager and the manufacturer's sales VP shake hands on a new pricing schedule. Two years later, the manufacturer sues you for underpayment based on the original written terms. Are you protected by the handshake deal? In most cases, no — and no-oral-mod