Is it legal to buy and sell fused magnesia without paying taxes?

Legal. When the merchants in the retail link are enterprises, both ordinary taxpayers and small-scale taxpayers need to pay the target price increase, so they must also include tax when selling goods, otherwise they will lose money. Secondly, if it belongs to individual industrial and commercial households, whether it is necessary to pay value-added tax is judged according to whether the monthly sales (monthly turnover) reaches the threshold set by the local tax authorities. Therefore, for self-employed, if there is no need to pay value-added tax in actual operation, as long as there is no loss, the sales price will be decided by the merchant. However, if you need to pay VAT, you should consider the tax amount, otherwise it will also cause losses.