That phenom is known as the "dealer's two-step". Here's an example. About 12 years ago, a young man laid off from his job brought his Remington autoloader deer rifle- in .308 cal. and with a good scope and mount, into a local crook who had a gun shop-known for preying on widows and bilking them out of their late husband's guns for .10 on the dollar- he told the lad- "If this were a .270 or .30-06, instead of a .308, I could offer you way more" The kid took the deal, and after he walked out with his cash, the dealer grinned at me, and showed me a foot locked full of military ball ammo for the M-14 (also M60) 7.62x51mm- aka- .308 Winchester. He told me he'd double his $ on the deal he just made with the unknowing lad-- So, if you want a M21 with 2 triggers, you pay the market price, if you want to sell one to a dealer or trade it up into another double, you'll get the "nobody wants a double trigger on their M21 now-a-days-after all, their single trigger is the best ever offered on any American mfg. doublegun" or some other similar line of horse-shit..
