Avis Budget Group Inc. investors were having their worst day in four years on Tuesday, after the car-rental company said it sold a record number of vehicles during the fourth quarter in a bad market for used cars, due to vehicle oversupply and a spike in interest costs.Meanwhile, the company reported fourth-quarter profit that was well above expectations, despite a surprise decline in revenue.“Currently, there is a considerable amount of volatility in the used-car market,” said Chief Financial Officer Izzy ...