Advice sought on sending a preamp from Canada to the US for repair and return

Nothing to worry about, declared value is not the same as insured value.  Don't confuse the 2. 

Mark off as a repaired item. Shouldn't cost you anything. Makes sure the company marks it likewise when sending back 

I would suggest reading this publication:

https://www.cbsa-asfc.gc.ca/publications/dm-md/d8/d8-2-10-eng.html
" Goods Returning to Canada Having Been Repaired Outside of Canada"

Near the end of the document, there's 'Addition Information' that has a phone number you could call if required.

While I'm opposite of you, live in US, amp and preamp Canadian. I've shipped these pieces to Canada for upgrades, always state on custom forms items are being shipped for repair. I always diy out of country shipping, major shippers make it somewhat understandable, done it enough now that I feel comfortable shipping anywhere.

I'd contact manufacturer, they should be able to direct you specifically on what you'll need. Otherwise go to shipping store.

I have bought from Canada, had a shipping damage claim, it’s tricky, i.e. UPS Canada (different name) is separate from UPS USA.

but not dealt with what you are concerned about.

1. I would include an info packet inside the box. copies of original documents, receipt when new, evidence original taxes ... were already paid.

2. printed copy of repair estimate, showing it is going cross border for that purpose

IOW, unlikely event they try to tax you twice, they open it up, find the evidence you tell them is there.

3. you using original factory packaging?

4. put in a second outer box, i.e. shipping insurance requires ’double boxed’.

5. clarify who buys the insurance, i.e. whoever buys the insurance has to make any potential damage claim. going? returning? if maker buys the return insurance for instance.

6. have maker include your original info packet inside with their completed repair bill added to that.

..............................
just to add:

Any seller who says ’local pickup only’, if you can get them to simply drop it off unwrapped at a local UPS office:

recently I pre-arranged with UPS: had someone simply drop off an unpackaged item to a UPS office I found near them. They simply told them it was for ... (my name). UPS called me with their price, took my credit card info, they package safely and ship.

UPS Canada was willing to receive in Canada, package and ship to me in USA, no hesitation.

The customs forms definitely let you specify that it's a used item being shipped for repairs. You should not have a problem. I'd suggest taking it to FedexOffice and let them fill out the paperwork for you. Go during the slower part of the workday when the location's manager is there and ask questions to ensure you're working with a rep who's got experience with the customs paperwork. Cheers,
Spencer

You're implying that your expensive pre-amp can't be serviced in Canada.
Not true.  You just need to find out where the good techs are.
My recommendation is to PM @anatech at diyAudio who has been fixing hi-end gear for decades and is also a moderator on that site.
He lives in Georgetown , Ontario