Just like a car, when it leaves the lot it's "used." Person to person it won't lose a ton of value but trade in at the dealer and it will.
I buy a lot of things on this website but I find that a lot of people want to close to what I could buy it brand new for. I guess everyone is different but for me it has to be worth my wild to buy it (used). Since most of what I am buying is impulse that might have to do with it too. lol
"New in the box never fired" is just code for priced too high. I don't care what a seller says. New in box has probably been stripped, cleaned, oiled, dry fired 1000 times, posed with in front of the mirror, and as far as I'm concerned... shot. If you're not an FFL and dealer of said gun... it's a used gun in great visual condition.
Also keep in mind lots prefer not to go through an FFL to avoid background checks. That is worth something to them. Different strokes for different folks. Will say again I always get at least what I paid or more when selling a firearm. Great investments.