Making the importing consumer pay the tax at the time of purchase is a big mistake.
In the first place, it should not be the Marketplace that assesses the tax due for an imported product, but directly the Brazilian IRS at the time of importation.
This opens an opportunity for many products to enter through the Post Office without taxes. And how is it possible to know which ones were actually sold on marketplaces and prepaid taxes?
If taxes are collected only at the time of sale, what about many items that enter tax-free, expecting the tax to be incurred on purchases from marketplaces, but intended for a sale at a physical establishment, or an ecommerce which is not marketplace?
If within Correios Brasileiro, there is no condition to tax 90% of the international parcels that arrive there, how to integrate the transaction of sale of an order with its corresponding importation and arrival?
This solution will open the door even more to the non-payment of taxes, and new e-commerces will emerge selling goods without taxes.