I can only speak to Australia as a destination and the simple answer is to be honest. Most parcels are x rayed so Customs will know that it is a knife. Calling it something else won't help matters. Call it a camping knife, pocket knife, hunting knife or whatever the case may be. I don't recommend combat knife or zombie killer or the likes as a description.
Declare the correct value of the goods. The threshold for duty here is $1000 and even beyond that value the duty is not that excessive. Valuing an expensive looking knife as $10 etc only makes it look like someone is trying to fool the system. Also creates issues if the item is damaged or lost.
Make it clear that you will label honestly and that the decision of Customs is the buyers problem and that no refund will be provided if the item is seized.
Insurance and tracking are about balancing risk and value to me. I would not pay $40 postage on a $50 knife but would carry the risk as a buyer and request a basic postage option. A $300 knife would be a different matter. Having said that I have never had a knife lost in the post and have never had a problem with international delivery in over 30 years of buying and selling.