They pretty much go begging for owners unless they're a riot configuration. Then everyone wants it. Many fine game guns are simply cut down to make them sell,,and they do sell well and for good profits for the work involved.
Unappreciated or just not up with the times,,what ever the issue is the M12 and the rest of the classic pumps and autos are just not good sellers. You can find a lot of fine examples for very good prices in that bunch. But don't expect to squirrel them away and make a million bucks. Just enjoy them while you can. It's a hobby after all.
That's why my Marlin 43T, Stevens 200 pump and 520, Rem 10T, Win 42, FNA5 and Sportsman 48 see a lot of range time. Could care less about values at this point. I just like 'em.