Will I Pay GST When I Get My Banknote Graded And Shipped Back To Me In Canada?

By random do you mean the government sometimes charges HST on the insurance value?

This situation is a really gray area .
The Government of Canada empowers
the CBSA to collect whatever taxes or duties
are applicable on the service that took place
in a foreign jurisdiction.
We use ANACS and NGC on a regular basis,
and have the coins returned to our US post office
address. They are insured for full amount only if
delivered to our US address .
We then walk them back into Canada and deal with
CBSA . We are always prepared with proper documentation,
ie. original paper work listing what we sent , a copy of the
grading service invoice and a proof of payment for the service.
What has happened over the last 37 years of doing this is
usually the border guard taking a Quick Look and waving us
through . Once in awhile they do inform us that they COULD
collect the GST , but not today !
Only twice have we ever been charged , once by FEDeX in 2013
and last August by a border guard , who decided the NGC plastic
Holders were quite valuable ( total charge $34 GST , BCST ) which
we claimed back . So I would just say to you , yes they can and no
they don't usually bother . Just be straight up and don't try telling
stories or CBSA can seize the goods and proceed with criminal charges.
Also if you do this on a regular basis it helps to get to know a supervisor
at the border crossing you normally use , can be quite helpful .