Federal money laundering statutes require the dealer or anyone who makes a cash transaction of $10,000 or more to fill out IRS form 8300. He needs more than your driver's license to prove your identity. The burden of complying with these regulations falls on the dealer. I've seen a small lot dealer go to Fed prison over it. His whole business was structured to sell to drug dealers though. If you go to the bank with 10k in cash, same routine, also if you show up to buy a house with over 10k in cash. It should not be a problem for anyone who has nothing to hide. These laws are not new. They've been in effect for at least 15 years.
If the vehicle you are buying is less than 10k, he should not need anything other than O.L. and proof of insurance.