How to protect yourself
When buying a used car, ask as many questions as possible.
Has it been in an accident? Have you inspected the vehicle? Have you serviced the vehicle? Who was the prior owner? Where did you get the vehicle? Was it ever a rental car? Etc. You you cannot ask too many questions. The Vehicle Code has express prohibitions against a Dealer making misrepresentations about a vehicle that "cause loss" to a consumer. Some cases can be handled very efficiently through Small Claims Court. Consulting a lawyer early in the process can be very helpful.
Another way to protect yourself is to write to your elected representatives in the State Legislature and in Congress. Some of the most influential and well financed lobbys are working on behalf of the automobile dealers and manufacturers. They work constantly to pass laws that make it possible to sell used and even new cars without disclosing prior damage to the consumer. Write your representatives and let them know that consumer protection laws need to be strengthened.