Customs are accurate in their functioning, however, if they charge the wrong amount for duties and taxes, it’s because of unavailability of tariff codes on the commercial invoice. In these circumstances, the customs officers will take a decision themselves about the category your items come under. Now, sender or receiver can dispute these charges with customs before delivery. You can do it by providing them with tariff codes for every product you’ve shipped; then you should inform customs that the goods cleared under an incorrect tariff code.