I assume you’ve done some work to this car? If it was me i’d bring all my reciepts and show all my time i’ve put in the car. Then i would say “look, this car was a pile of shit when i got it, i have XX time in repairs and XX monies. If you want me to pay tax on a higher value i would gladly do so if you pay for the repairs it took to get the car to the better condition.”