I've been in business for half a century and the first thing you learn is you play by the rules, you cultivate your friends because you trust them. Those you don't trust, it's simple dont do business with them, there are a few that I simply will not trade with Id rather sleep well at night.
Often business partners leave a firm, because they disagree with the company policy and set up on their own, sometimes they prosper, maybe not. What they will not normally do is trade with the old company they will often compete using the contacts they have.
This is what the Brexiteers want to do compete with the EU for better trade deals AND trade on favorable terms with them. The EU are saying OK you can do that, but you obey our rules, as they do with EFTA members. The present quarrel is about the NI backstop and UK wanting a unilateral end point, EU are never going to agree to that, it would mean that UK could end trade negotiations whenever it wished.
The trade negotiations due to begin in April will set tariffs and quotas across all sectors including financial services, good will is essential because compromise is needed and "nothing is agreed until everything is agreed" for example financial services against fisheries, or food products against cars, that is going to take many years WETHER OR NOT TMs deal is agreed.
I mentioned fisheries, yes, we may get "control" but to win concessions in other areas, quotas will be traded with Spain, France and others. Anyone who does not accept that is living in La La land.
One particularly brainless politician said yesterday that we would not be paying the £39bn leaving cost, oh yes we would, it would simply be added to the tariffs imposed. Total pratts, the public actually believe such rubbish.
For the record, TMs deal is awfull, I would much prefer to Remain but if it is No Deal I will live with it but the poorest in the UK will suffer most.