> How do you know he didn't buy the car from the thief?

If you're caught with stolen property, particularly a vehicle that has a title, I think the burden is on you to prove you thought you bought the car legitimately. Show a bill-of-sale, signed title, or any other evidence of a transaction. Particularly when that evidence includes identifying information of the seller.

Bank records are readily available, large cash transactions as well.

Well then he's in possession of stolen property, which is also a crime.