Goods and services do not flow completely freely among countries, even among those with excellent relations. Countries put up barriers to trade for a number of reasons. Sometimes it is to protect their own companies from foreign competition. Or it may be to protect consumers from dangerous or undesirable products. Or it may even be unintended, as can happen with complicated customs procedures. Tariff barriers have been reduced considerably over the past few decades but other obstacles remain. Getting rid of unnecessary trade barriers would give a great boost to global economic welfare.
“Would you mind opening your suitcase?” Your heart sinks as you picture that ...