When we had a [Brexit] deal, I thought, we're saved all the rigmarole and hassle, it'll work sweet as a nut, but it hasn't happened," says Mr Flannigan. Instead, he says, it feels like the clock's been turned back 30 years
People really don't have a "sweet as a nut" clue do they?

Yes "30 years" and worse ..because you are now outside the Single Market & "worse" outside the Customs Union too . You're now trading under conditions more like Belarussia into EU without the customs & logistical capacity to handle the volumes. Your business will most likely fail

This was always so ..regardless of the "deal" esp with "87% of Berwick Shellfish's £1.7m sales go to France, Spain and Germany"
Next....
"The real test for me is the next two to three weeks, as inventory is depleted and orders increase," says Mr Munro.

"He thinks there's a window of opportunity now, for the authorities to fine tune the system before volumes are ramped up" .. "fine tune" Oh FFS...!! wake up.

The BBC report a litany of businesses not understanding the "deal" was always going to mean being outside the SM/CU

"Mr Dormer fears the "massive amount of aggravation" could mean business partners on the continent start to look elsewhere.".....errrr ...yes.

Note how though the report leads with a suggestion of EU "pettiness" https://www.bbc.com/news/business-55638969

It gets me to see happy smiling faces on people about to have their business lacerated, decimated or destroyed.

..and again not "new" rules but *existing* rules for non EU (non CU/SM) countries.
Hard to see where the "opportunities" will be with these "new" rules