Lara owns a used car lot. She emails Seth, a used car wholesaler who has a huge lot of cars in the same city. The email reads, “Confirming our agrmt—I pick any 15 cars from your lot—30% below blue book value.” Seth reads the email, laughs, and deletes it. Two weeks later, Lara arrives and demands to purchase 15 of Seth’s cars beneath marked value. Is he obligated to sell?