MetLife will pay a $50,000 penalty and refund an undetermined amount of money to customers to settle allegations it imposed costly surcharges on Massachusetts drivers who were found not at fault in auto accidents. In detailing an agreement reached with Metropolitan Property & Casualty Insurance Company, state attorney general Martha Coakley said Tuesday that some custoemrs who filed accident claims were improperly penalized even after a state appeals board had ruled they were not responsible for causing the crashes.