There is not one single thing that is correct about that article, never mind the incorrect calculations.
Have they decided where they are going to buy these items from, have they already done the trade deals, tariffs aren't charged on the internal transportation, packaging within the UK, shop profits, staff salaries etc etc etc etc etc.
There are no tariffs if the items are bought from within the EU at the moment.
I especially like the one about the LG flatscreen TV where there currently is no tariff because of the EU trade deal, but there will be tariffs when the UK leaves, none of it makes any sense.
How do people believe all this crap, whoops, sorry forgot, Brexiters are highly intelligent people.