If the seller is not the owner on the title and you agree to buy the car say: "Please bring this person here so he can identify himself and sign a bill of sale."
If the answer is anything but "Yes" turn around and walk away.
If you want to save yourself a wasted trip, ask the seller on the phone "Are you the owner on the title?" If not, ask that the owner be present when you go see the car. If you get some story (there's always a story) just say not interested and move on to the next ad.
Plenty of cars in CA owned and being sold legitimately.
If you do want to buy the car, do not believe anything the seller tells you about it. Have it thoroughly checked out by a mechanic before you hand over the money.
Carefully study the CA smog requirements (google it) and make sure they've been complied with.
Always check the price guides before negotiating:
Kelley Blue Book
NADA
Edmunds
They all have websites.

