Because of the EU single market, customs tariffs don’t arise where goods are bought and sold between EU countries. The tax arises only where goods are directly imported to the bloc. Although the UK left the EU just over six months ago, the Brexit withdrawal agreement made room for a transition period so that, for 2020 at least, the UK is treated as part of the EU for customs purposes.  A timely reminder of potential financial effects of customs duties on an Irish trader is to be found in Tax Appeals Commission decision number 137 of 2020 involving a customs…