Some people, depending on their profession can get away with the "drive a car into the ground" approach to vehicle ownership. If you can suffer a short-term loss of transportation it saves you a lot of money on car payments. If you are a traveling consultant, you simply cannot. You really need to always be in a newer, reliable vehicle. Preferably with some kind of roadside assistance like AAA.

Your clients will understand if you've been delayed by either an accident or a flat tire. But they will not want to hear why you didn't show up becuase your '98 camry with 230,000 miles finally blew its head gasket. They're going to think you're unstable/unreliable and you will most likely not be invited back.