A prosecutor has the burden of proving beyond all reasonable doubt the elements of any crime, therefore the prosecution would have to prove that either you knew the car was stolen or you should have known.

Certain crimes require that you specifically intend to do a crime. These are called specific intent crimes. Other crimes require only that you intend to do some act. These are called general intent crimes. The difference is whether or not a certain crime is a specific intent crime or a general intent crime. Most theft crimes are specific intent crimes. You can read more at: www.AggressiveCriminalDefense.com

A buyer who genuinely and reasonably believes the car was not stolen would not be guilty of a crime. He might appear guilty, though, in which case he could still be prosecuted. He might even be convicted. Such things do sometimes happen to innocent people.

But there are consequences beyond potential criminal liability. If the buyer purchased the car from someone other than a bona fide dealer in automobiles, he would not become its legal owner. The person from whom it was stolen would remain the legal owner unless and until it was sold by such a dealer. Your hypothetical buyer would have to surrender the car if the rightful owner demanded it. He could then sue the seller for the return of his purchase price, but if the seller knew he had no right to sell the car he will probably be hard to find. And even if the seller can be found, there's a good chance he would not have much money with which to pay a judgment.