I would like to create a tax that allows only profits to be taxed. Why ? Because in France there is a tax called "Margin VAT" applied to second-hand products or only the profit is taxed. Example I buy a second-hand product for 100€ and resell it for 200€, only the profit (so 100€) is taxed at 20%, therefore a tax of 20€ and not 40€. Thank you for your help.