The fact that some hazardous items (as defined by RM) are being delivered is a red herring. Some will slip the net, others may be from business customers.
In the latter case if they’re shipping hazardous goods they should have someone competent to understand the regs and make the decision it’s safe to ship. A private individual doesn’t have that qualification and nor presumably do the counter staff, hence these ‘odd’ catch all categories of what is considered hazardous.
And I think it reasonable that once it is shipped if it is later caught and assessed as hazardous then no way should the RM be expected to onward ship just because they accepted it by some vaguely untrained counter staff member.
What is clearly unreasonable to me is what they subsequently define as hazardous – once intercepted then surely it’s not unreasonable that someone in each locality has the skill to make an informed judgement of what is and isn’t hazardous, and if it isn’t then they can onward ship with a perfectly rational explanation of why it’s delayed (as per example above). And if they won’t onward ship because it’s genuinely hazardous (but not dangerous) then it doesn’t become ‘theirs’.
With the system as it is, it seems to me they’re advantaged by making the rules as they are, not providing the skills locally to fix this locally, and then profiting from the rules in a way that makes it beneficial to quarantine as much as possible, which while hidden behind contract terms is morally theft in my book. And with the rise of the semi-business eBay type customer – not big enough to be able to cover their own regulatory requirements but sending enough to be significant – this looks like a gravy train they’ve enjoyed for too long.