Why not? I know some people put $0 for the 1D Mk2 when shipping.
The only problem is that you cannot get any insurance if you don't put the really value.
You have to take the risk if it gets lost during shipping.
I don't think it's wise to declare very low value for expensive equipment shipping over the boarder just for the sake of saving tax. It does not worth the risk. Bad things do happen during the shipping/delivery (e.g., it may be left at your door and when you get home it's gone). Also, the custom officer is no fool and they can/do open the package to check the item. They will put the real value regardless what's declared by seller and you have to pay tax anyway.
From seller/sender, it is a serious offence if they were found declaring false values for the goods they ship out so most seller don't do that.
I second shipping with USPS. Bought 4/5 items from US through USPS and only for once that the package was lost but later found and returned to seller. Out of all transactions, I got lucky for a US$300 item when the custom forgot to charge me tax.
Happy shopping.
One final word: don't visit Buy & Sell forum of FM too often. You will get poor quick.