They got hosed, because that is definitely not how the law works anywhere. No state can impose sales tax on property purchased elsewhere while you were a resident of that other place. The only way that scenario would unfold is if that vehicle was not registered in the previous place and you somehow could not show you paid tax in that previous place, making it look like you, as a California resident, bought a vehicle in another state. The law is like crystal clear on this. The fee calculator Random posted earlier even has an entry for "Use/Sales Tax Paid*to Another State" so you don't get taxed twice. Either your family talked to the dumbest DMV employee in history (totally possible) or they didn't read the form. Or, I guess, they never registered the vehicle wherever they came from and lost all the paperwork associated with the purchase. I guess that could happen too. I have brought numerous vehicles in from out of state, and never been taxed twice - you just fill out the box "use tax paid elsewhere" and - depending on the numbers involved - submit proof.