"So, you got a package that was marked "Return to Sender"? Or, some other form of notification? Sorry, I am just trying to understand."
No, the vendor ships, it hits customs, and goes back right back to the vendor, who alerts the buyer.
Ordinarily, if something is opened and assessed, you pick it up at the post office and have to pay to do so, GST, HST, tobacco (per gram usually) taxes, handling fees, etc. This idea of these fuzzily declared packages just being outright rejected is new in my experience. Don't know if there's a policy change or what.
Packages are also abandoned or Returned to Sender (upon non-delivery) depending on what shipping method you pay for.