Last time I checked, here in TX they go by book value now on old(er) cars because too many people had a 10+ yr old car that their friend sold them for $200. Back when I had my Caravan, this kinda sucked because I honestly did pay $200 for the vehicle! Instead they taxed me on book value of $1300. I forget the exact amount out of pocket, but it wasn't too painful.

I always wondered if this would still apply if you had a notarized receipt from a dealer that you paid well under book.