Duping isn't a thing in D2R. Not saying it isn't possible there was that one instance, but it was a moronic scam and the item instantly disappeared.
Look at the sellers, if they could make FREE runes, then why are they selling average botted gear at the same time? Sure there are a few who open rune shops here and there they're likely those who RMT bought mass runes to resell to stock on FG to trade more easily.
They did the same thing in LoD. They don't bust out the perfectly rolled gg shit right at the start. They off load things very slowly as ladder comes on.
They dupe pskulls, runes to cube into legit runes, and other crafting recipe gear. They have bots running this stuff 24/7. It takes a long time to get something incredible unless you're OnAir or something equivalent.
They are absolutely still exploiting this game and exploiting the hell out of it. OnAirs pskulled rolled items in LoD AND d2r prove that fact.