That has to be one of the most difficult agencies to get information from. On other matters I've had to call them, they feign total ignorance of what I am asking and when I slightly change the wordage to match the bureaucratic speak, suddenly they remember an answer or a specialist sitting 4' away. There simply is no way to get good advice by 'calling customs". I've had customs officers question me why I was declaring a $1500 canopy I was importing, other times they will make a big deal out of something that would seem trivial
When importing in to the US several years ago, it was important to have a notarized bill of sale (I believe that was a Washington State requirement). Not a big deal to find a notary in the USA, but very formal in Canada.