If you'll allow an observation from a newbie . . .
My theory is that at a certain age, men begin acquiring the things they longed for when they were kids. The things they saw their dad and granddads use when they were children and young men are the things that hold their fancy for the rest of their lives. They can't afford to buy these things as they begin their working lives and family rearing years but they never forget. The shiny, fast, powerful things that struck their imagination when they were young continue to call to them throughout their lives. Someday, when the kids are grown, the mortgage doesn't seem so daunting and the income rises, they begin acquiring the things they've always wanted.
Consequently, men in their buying/collecting prime aren't buying the hot items today. They're buying the hot items of 25-40 years in the past. This is true for guns as well as cars and many other consumer items.
This explains why men of a certain age bought Model A Fords when they could afford a mid-life toy, their sons bought '57 Chevies, and those men's kids bought 60'/70's muscle cars. Each was scratching that itch that has plagued them since they were children.
The same is true of guns. Some men get teary eyed over Model 12 and 15 shotguns while men of a different generation think a Remington 1100 or a Browning Citori is the be-all, end-all. Will tomorrow's big spender long for some camo, plastic thing with 3.5 inch chambers? Who knows?
The corollary of all this is at a certain point there is declining demand for products of a certain age. As men die, move into nursing homes or simply scale back or end their collecting activities, there are fewer buyers for the old items that men once treasured. The next generation does not share their love for that particular era and aren't nearly as interested in buying the same things. A couple of generations later there is almost no interest.
What's the demand for Model A Fords these days? I don't know but I suspect it's pretty soft. Only the best condition, most desirable variations bring top money. The same thing happens with guns. Common or average condition examples languish on shelves and only the best pieces retain value.
At some point you can't hardly give away the rough or common examples. My prediction: In 20 years, the market will be flooded with Model 12 and A5 shotguns. You'll be able to buy all you want for next to nothing.
How all this applies to double guns, I'm not sure. Rare, exquisite things will always have a market. Common stuff, much less so.
