I live in Hawaii. I bought a used Tacoma from a Toyota dealer in WA ( a few years ago). They waived the sales tax because I was not a WA resident. How did I prove that I was not a WA resident? I provided two recent Utility bills from Hawaii for their review. That's all it took to satisfy their concern.
While CA collects sales tax even on non-residents, most states will waive the sales tax when you provide proof you are not a resident. They know you are going to have to pay it when you go to register the car for tags.
Before Tesla Honolulu had their dealer license, we owners had to navigate the tax payment and registration process individually. We mapped the process for those coming after us. The car arrived, we collected Bill of Lading, Title, Safety Inspection and went to Dept of Taxation and paid our excise tax, then with that receipt we could proceed to DMV for the registration. As an owner, we had to show we have paid the excise tax before DMV would allow us to register the car.