The burden of proof still lies with the companies selling those products and services. The only difference is that they currently prove conformity to the UK government and the EU trusts that conformity by proxy. The burden of proof is still the same.The EU isn't a socialist institution and the Single Market certainly isn't but we'll ignore that for the moment.
The friction is caused by the need to prove that you meet those standards and the time and expense of that process.
Within the single market this is taken on trust and there is a single recognised arbitrator for settling disputes.
Outside of the single market, a company wishing to export to the EU will still have to meet those standards but will have to prove that they meet them every time that they export. They can also expect delays whilst those goods are inspected when they enter the EU.
Divergence would also increase the costs on producers because they would have to have separate processes for goods destined for the EU and UK whereas now they only need one.
Services are different because there needs to be equivalence in regulatory regimes. We currently have this within the EU. Outside and with you advocating regulatory divergence, this would be lost.
All of this wouldn't hit all sectors equally. But it is complicated and another barrier to a quick resolution and I am yet to see anything other than speculative benefits of a policy of diverging from EU standards and regulations.
This should be a net win for UK business as currently the UK enacts EU legislation far more strictly than many other EU countries. This is something that's very common in my industry and many of those related to it.
Whenever our MPs put forward complaints on behalf of the UK, the response from the EU is essentially a shrug along with something similar to "It's Spain/Italy/rural France, what the fudge do you expect us to do?"