A Hard Brexit means we are out of the Single Market and Customs Union.
When Hard Brexiters talk about a Free Trade Arrangement – we would still be out of the Single Market and Customs union. So this would mean that there would not be frictionless travel and there would have to be border checks between the UK and the EU.
For example, currently our meat has to be the same quality as the meat in France, Italy, Germany and all the 27 other EU countries so that there do not have to be so many checks on exports from the UK to the EU. If we import lower quality meat (because of a unilateral trade agreement between the UK and the USA, say) then the UK could be used as a smuggling route into the remaining EU countries and so the EU would want to prevent that by checking.
In fact they would have to prevent it by law because of agreements and treaties made over the last forty years. So the EU are not being difficult when they point this out to the UK.
So the EU would have to check imports coming in from the UK. This would make the administration costs for UK companies much larger than they are now and make our products more expensive than competitors in the EU (or companies would have to swallow the costs and cut profits drastically). This would mean many small and medium sized businesses would go out of business and many large enough would relocate to be within the EU. It would also mean large corporations from outside the EU who have invested here would likely move out of the UK also (large corporations like Nissan for example have established themselves in the UK to have access to the single market).
When food is imported into the EU vets check the food to make sure it is up to standard. This costs money in terms of labour and land to do it. If the UK leaves the single market and customs union, the EU will have to carry out more checks.
The lens we are looking down outlined by Sarah in her latest letter and that was covered last night in the first 10 minutes of Inside Out South West are describing the problems we will face in a Hard Brexit scenario and will be worse than this if we go to a No Deal.