How will trade work between North and South post-Brexit?

And so the softening up process has begun - there will be checks on goods crossing the border, the only matter to clarify is where exactly, writes
Fine Gael ministers have for the first time confirmed in the event of a hard border checks, tariffs or agri-food inspections will be needed somewhere to protect the EU's trading frontier. But they continue to insist these checks won't take place on the border.