I have sold major items person-person many times, and besides certified funds (from a bank ideally, or cash) that you take to your bank to verify FIRST, you would sign over title AND provide bill of sale, signed by both parties.
HOWEVER---I don't live in CA.
You'll dislike me for saying this -- but you should figure all that stuff out FIRST before having sold it. Know the process for your state. Have a plan. Know what types of payments you'll take and HOW you will handle them. Contact the DMV (or website) of your state and see if they have info. Again, I can't imagine that it's any harder than Bill of Sale, Title signed, and certified funds.
