"The average man does not buy his gun as an investment, but as a tool to use afield". Not word for word, but close to what the late Captain Paul A. Curtis wrote in 1934- in his book "Guns and Gunning". Many gun "collectors" use the theory of the "greater fool"- they buy a Parker or a Holland & Holland today, at market pricing reflecting on grade, gauge and condition, and plan to move it to another party "down the road" at a mark=up, same philosophy high end gun dealers employ I should guess.
If you want investment advice, get close to Warren Buffett, and stay out of the gun market. KY John has just penned "words of wisdom"-- and older gentlemen gunners, like two of my friends from a pheasant hunting club where I shoot, have passed on, their children and grandchildren do not hunt or shoot clays or paper targets, so the guns go through the auction "mill" and the net cash is divided with the proceeds of the estate.
I only buy used older guns that meet these criteria: (1) They must earn their keep- they are all meant for shooting, or as Hemingway once remarked: "A gun is to shoot with"!!(2) They must have been proven to hold up in the field without breakdowns- Model 12 and 97 Winchester pumpguns, Belgian Browning A-5's, LeFever Nitro Specials, etc.. (3)They must be priced, depending on condition, close to the current Fijestad Blue Book range--and (4) They must be in "wear with care" condition- I stay away from the Del Grego and Turnbull "showpiece" guns, like my hero Hemingway, my guns are all working class, show use but not abuse, and are, like an old friend, 100% reliable. (5)In centerfire BA rifles, I stay with the std. calibers, avoid the wildcats and short-fat Magnums- better re-sale and cheaper ammo. By that I mean, in BA rifles,: .270Win, ,243Win, 30-06, .308..300 Win Mag, .338 Win Mag and .375 H&H Magnum ( my only exception is a G&H custom BA in .35 Whelen, but Remington and others offer factory ammo for this great "Wildcat in cal. 30-- I passed up a near mint 1939 Winchester M71- as they were only offered in .348 Winchester, and that ammo, around my neck of the woods anyway, is fairly scarce and pricey. In shotguns, 95% 12 gauge- I hate to pay the big premium for the 16 and 28 gauges, and like Nash Buckingham, I detest the dinky .410-- You'll' get a better deal in today's used double gun market if you shop for a 12 gauge, and pass up the smaller gauges, at least in my experience. I am not a college man, but I have read both Adam Smith's tome : The Wealth of Nations- so I think I grasp the supply and demand theory-- The major double gun companies made more of their guns in 12 that in all the other gauges popular at any one point in time.