I too had to pay sales tax. Look at it this way. I buy something for $100. I pay $9.5 in sales tax. Now I turn around and want to sell it. I can't sell it for 109.5 because the buyer from me also needs to pay 9.5% sales tax. And now that the car is "used", I have to sell it for less than 100 so let's say I sell it for 90$. The new buyer pays 9.5% of 90 (approx 9$ in sales tax too). So even though I sold it only for 10$ less, I lost 19.5$ in that transaction and CA got paid 9.5 and 9.0 = 18.5$ is sales tax.
Basically I lost the 9.5$ I paid in sales because I barely used the car. In rest of the world, they use Value Added Tax (VAT) and because I didn't add any value when I sold my car, the new buyer won't pay any tax so I could technically sell my car for 105 even though he can buy from Tesla for 100 (and then pay 9.5 in VAT - so it is still cheaper for him to buy it for 105 from me).
