Same deal here in CA. You have no benefit of lowering the actual sales price. The only benefit is to the buyer who will pay taxes on the stated sales price. Taxes are paid when the car is registered with the appropriate administrative agency. (DMV, SOS, etc.)

When you do sell the car, make sure to do the following:

-Make sure the funds clear the bank - Cashier's checks can be forged.
-Make a photocopy/scan of the person's PHOTO ID - Preferrably a driver's license.
-Pull a draft bill of sale for the vehicle and list the following: 1. both parties full incormation/address/phone #/DL # etc.; 2. year make model vin and license plate and mileage; 3 vehicle is sold as is where is with no implied/expressed warranties; 3. sales price' 4. signatures signify release of all liens and liabilities for the aforementioned vehicle; Signatures of both parties with date of transaction.

Make 2 copies and have original signatures on both.