@stech - suggest reading through these FAQs for all your questions
https://www.irs.gov/credits-deductions/used-clean-vehicle-credit
Does $25k applies to used car? Because new Tesla is $40k. For used cars, sales price has to be $25,000 or less to qualify for the tax credit,
$8k tax liability is before withholding or after all adjustments/credits and total tax due must be $8k? I think @Critter-3 mis-typed. The maximum tax credit is $4000 for a used EV. It's 30% of sales price, but a maximum of $4,000. The tax credit is non-refundable, which means that Line 22 of Form 1040 BEFORE applying the credit must be at least $4,000 to capture the entire credit.
I did buy it from used dealer (not Tesla) - great that is part of the requirement for the EV credit on a used car. However, Tesla is not on the list of qualified used EVs
https://www.irs.gov/credits-deductions/manufacturers-and-models-of-qualified-used-clean-vehicles
