The sales and use tax for tangible items is treated differently depending on what class of items are purchased. The tax you would be paying on the auto, according to AZ is actually a use tax. The tax on a bed is a sales tax. In fact, in some states, such as NJ, sales tax is required to be collected and paid for items purchased at flea markets, garage sales, and flea markets. Though it is required, most states do not have the means for enforcement for garage and lawn sales. However, in NJ, PA, and other states, the sales tax representative is surveying the flea markets for compliance.
I called the AZ assessor's office and DMV today to verify the information. The response from both was that the tax, if any would be determined at registration.
How would they know? They would know because when you register the vehicle, they run the VIN numbers. When you title it, they will see which state it came from, and they will know if it is a state that taxes car sales or not. They would tax you on your purchase price.
One of our clients in NY had a boat that the state of NY came for the sales tax. The boat was purchased 10 years ago in Connecticut, second hand. He took the boat to Florida where he registered it. Then he brought it to NY where he docked the boat. 10 years after registering it, NY came for the sales tax.
It is the same kind of thing for you, with your car registration. If they do not charge the sales tax at time of registration, and years later on an audit, they discovered sales tax was not paid on the vehicle, then they will come for it, even if it was bought used.
States are really going wild on the sales tax issue since a test of auditing and the law in 2003 of the ability to collect these kinds of sales tax.
The laws on automobiles and sales and use tax has been common since the 70's.