I think it is safe to assume that we will be able to import from them. I can't see them applying tariffs other than VAT. The other aspect of course is where to get the stuff from anyway? If some one imports at the moment apart from tiny amounts on a few things the main cost increase is VAT.
VAT on EU imports is a cashflow issue not a cost issue. VAT registered businesses importing from the EU are invoiced net of VAT, but after the transition VAt will be charged and claimed back.
The major problem is not tariffs but trade friction, its a huge barrier to trade.
Brexiteers fails to understand the huge benefit of frictionless trading inside the SM.
that friction will include: customs declarations, rules of origin checks, Sanitary and phytosanitary (SPS) measures etc etc
list of borders operations:
Functions Related activity Revenue collection
• Collection of customs dues, excise dues and other indirect taxes
• Payment of dues and fees
• Management of bonds and other financial securities Safety and security
• Security and smuggling controls
• Dangerous goods
• Vehicle checks
• Immigration and visa formalities
• Export licences Environment and health
• Phytosanitary, veterinary and hygiene controls
• Health and safety measures
• Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) controls
• Ships’ waste Consumer protection
• Product testing
• Labelling
• Conformity checks with marketing standards (for example, fruit and vegetables) Trade policy
• Administration of quota restrictions
• Agriculture refunds
• Trade defence
• Customs agreements
And lets not forget the issues surrounding regulatory divergence which will cause significant problems in some industries such as pharma, chemical, aeronautical etc etc
when the transition ends the Eu will no longer allow the UK to self certify its CE testing: so it will become difficult for EU businesses to import from the UK. the administration pain will mean they may well look to find a alternative supplier withni the single market.