As a "business", you can charge the expenses against the revenue. The difference is considered profit and is taxable income. Normally you would deduct the tax paid on the parts on an ongoing basis (monthly, quarterly or whatever) and when sold the buyer would pay the tax on the selling price when they register the vehicle.
In the case of a non-business sale, you're pretty much at the mercy of the state. But in reality, how much tax will you actually pay? Its all based on your income and the tax bracket you fall into. And I think just about any auditor would agree that you have some portion of the value to deduct. For example, if you sell a nice hotrod for $40k, there has to be a reasonable portion of that where tax has been paid on the initial purchase as well as any parts that added to the value - a $40k hotrod doesn't materialize out of thin air !!
A government tax auditor once told me "if you ever get audited, take the case to court" because they initially go for the throat to scare the crap out of you so you don't do it again. The majority of the time the amount gets reduced to more realistic amounts - people do make honest mistakes!
In the case of a non-business sale, you're pretty much at the mercy of the state. But in reality, how much tax will you actually pay? Its all based on your income and the tax bracket you fall into. And I think just about any auditor would agree that you have some portion of the value to deduct. For example, if you sell a nice hotrod for $40k, there has to be a reasonable portion of that where tax has been paid on the initial purchase as well as any parts that added to the value - a $40k hotrod doesn't materialize out of thin air !!
A government tax auditor once told me "if you ever get audited, take the case to court" because they initially go for the throat to scare the crap out of you so you don't do it again. The majority of the time the amount gets reduced to more realistic amounts - people do make honest mistakes!