No. At customs, there are hundreds and thousands of different tariff categories and rates. The actual tariff rate depends on the kind of goods, the material they are made of, the origin of goods etc. In order to offer a technically feasible solution, we work internally with an average value of the customs tariffs. And even if in some cases the import duties calculated by UK customs should be higher than our internal calculation that was the base for your shipping cost at checkout, you will never be billed extra for that; we cover the difference.