//Our lorries are being stopped at Calais so that proper checks can be made on the contents of the lorries,every single box of seafood has to be checked,every box has to have the proper paperwork.One mistake and the whole lot has to come back to Britain.//
That's quite true. But the Agreement does not provide for such comprehensive and widespread checks. It relies upon trust (by both sides). The idea is that UK traders should be trusted to abide by the rules (which they were bound by up to the end of December) and that only cursory and random checks are made.
The underlying problem is that the EU and its puppet members (particularly France, in this instance) cannot be trusted. All their proposals and procedures are accompanied by threats. Nowhere was this more apparent during the Brexit negotiations but it is apparent elsewhere. They are currently involved in a war of attrition with Switzerland; that country has a number of bespoke agreements on individual topics with the EU. This does not suit the Euromaniacs; they want Switzerland to sign up to a comprehensive, all encompassing relationship which will give the EU control over many of Switzerland's affairs. The "offer" is, naturally, accompanied by the threat that the existing agreements will be rescinded unless Switzerland agrees to the EU's terms.
They cannot even be trusted to treat their own members in a fair and equitable manner. Greece had a technocrat government installed in exchange for the EU bailout which was necessary principally because Greece was fraudulently allowed to adopt the euro even though they came nowhere near to achieving the qualification criteria. They were given too many euros for their drachmas which enabled them to buy more German goods than they could afford. Some EU members are clearly and openly more equal than others.
The Withdrawal Agreement was designed to ensure frictionless trade would continue. The UK made a number of concessions that a sovereign nation should not be subject to (such as imposing an internal customs border) in order to secure that agreement. Yet here, just a month in, in is quite clear that the EU has no intention of adhering to that deal.
You do not do deals with bullies to stop them bullying you. It doesn't work like that - you will be bullied all the more. We should have made no agreement whatsoever with the EU. Any problems arising now are purely as a result of the EU flexing its muscles. It is doing so in France and it is doing so in Northern Ireland.
The EU is not interested in seeing free trade. It is not interested in the wellbeing of the citizens of its members. It is simply a cabal of power hungry individuals intent on imposing their will on supplicant member states. The very best thing this country will ever have done is to leave the EU and the more it distances itself from our "friends in the EU" the more it will prosper. A few people may get damaged on the way but that's an unfortunate consequence of becoming involved with untrustworthy bullies.