take care.
If you undervalue the shock on the declaration, but you insure the package correctly, they will put 2 and 2 together. Mate of mine was left having to explain that the fork he'd bought was actually a warranty repair thus had no commercial value but did carry a replacement value. He got away with it, you may not be so lucky
how used is the shock? I'd look around first and make sure you're getting a decent price. Used bike kit I would expect to pay half what I could get it for new. There's nothing stopping you from ordering a new one from Canada / the US and factoring in the duty.