Actually I can confirm, knowing a couple gold farmers that there is no actual Dupe on the Sand, or other Vial of the Sands mats as people have been saying... but what I have learned is that they have found that they can actually buy up these vendor mats and put them into a guild bank as a way of storing their gold... apparently if they do this and they don't have a current buyer, they just load up the guild bank with more and more mats, and when the toon gets banned, all they need to do is make another toon and get it invited to the guild because blizz, for whatever reason, is not clearing out guild banks mats, just gold. For now Blizz hasn't caught on at least, or they are ignoring it.
it is a way to ensure that their gold is not going to be taken away, so they can get 50 accounts banned, but all their gold is still there on the server. They might lose some gold in the sale, but the overall loss is not as high as how much gold they were losing to accounts being banned. Also, when they finally do get a buyer, selling at a massive undercut from the vendor means instant sales, which in turn means fast delivery to the buyer. I have bought at least 200+ sands so far from 2 different farmers,, have made 15 or so vials with them and I can massively undercut competition with a huge profit, allowing me to sell vial of the sands rather rapidly, compared to before when I was selling for 40k+ and getting maybe 1-2 buyers a week... at 30k price I am still making like a 10k-12kish profit and no one is even competing against me cause they think I am selling at a loss...
I have even had people get mad at me asking why I am selling at a loss and I just say that I got ambitious and bought a TON of mats thinking I was gonna get rich and realized I was dumb and just trying to clear them all out