How do I spot a tourist trap restaurant in Italy?

Five signals, any two of which mean walk on: a menu translated into six languages, photographs of the food, someone standing outside inviting you in, a location with a direct view of a famous monument, and "spaghetti bolognese" on the menu — a dish that doesn't exist in Italy. Add these: a menu the length of a novel, meaning nothing is fresh, and being open continuously from noon to midnight. What you want instead is a short menu that changes, a handwritten or printed-today sheet, no English, and Italians eating at 9pm. Walking two streets away from the monument usually halves the price and doubles the quality.