The CBSA does make errors themselves. They are not perfect. Nowhere does it say that once they clear an item, they can't call you up 2 weeks later and demand that you surrender it. Agents are not always the best trained to recognize every sort of contraband. This is where we as a self-regulating community come into play.
I don't know jack shit about textiles. I know nothing about importing food either. They have loads of regulations when those items hit the border. If I was an agent, I wouldn't know what the hell I was doing with most of that stuff most of the time. The average CBSA border agent is in the same boat. He's likely an under-paid civil servant that has to know a little about everything, but not alot about anything in particular. This is likely the reason that guns do make it, even though they've been inspected.
Items that arrive via air or ground at a CBSA warehouse will be inspected by someone versed in the Firearms Act. This is why they don't make it, and why parts even can be problematic.
So, really, what we are asked here is for specific circumstances where the border agent failed to do his job properly and allow prohibited devices into Canada. Answering this question for the OP is not what I'd want to be doing.
Can anyone see where I'm going with this?
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.