The idea for this article is born out of teaching EU law and preferential trade law in a post- Brexit UK. The article has several aims. First, it challenges the ‘standard model’ of regional economic integration by presenting five case studies from and around the EU. Secondly, it provides analytical clarity for concepts such as ‘free’ trade, regional integration, and border checks. The article argues that ‘free’ trade should not be confused and equated with ‘frictionless’ or ‘borderless trade’. Thirdly, the article is meant to be a teaching aid for those who teach regional economic integration, preferential trade, and EU-UK relations post-Brexit. Finally, the article answers a very simple question: what exactly is checked at a country’s border? In addition to the most up-to-date information gathered from primary legal texts, government reports, academic writings, and the websites of various border agencies, the information is crosschecked by conducting conversations with traders, joining a Facebook group for lorry drivers, as well as sending inquiries to and receiving answers from Norwegian Customs, the Romanian Customs Authority, and the Belfast Border Force Team.