"Eye witness" accounts that aren't actually eye witness accounts. In this case you don't have "eye witnesses" btw. You have people who believe in duping and tell you that it happened because they "saw it" with no proof, and you have people who say "Oh yes I duped." again with no proof. That's not proving anything. If this was good enough then we could conclude that all cryptids (big foot, nessie, etc) are real because people the world over have claimed to have seen them. Yeah doesn't work right? Doesn't work here either.
Market anomalies that happened near the ends of at least three expansions with gems/raid mats/very specific mounts. Weird? Yup. Proof of duping? No, not by itself.
Forum discussion isn't evidence of dupes. In Vanilla WoW there was forum discussion on every relevant forum about how Ony suddenly casts Deep Breath more. The popularity of urban legends doesn't make them true. Widely held beliefs aren't evidence either.
Making excuses for why there's no video evidence isn't helping your case. This is the internet, you can find videos of WoW from 15 years ago. Why is this one specific thing the exception? It just all magically disappeared from the internet. I'd also like to remind you of the time in D3 that Kripparian convinced people that a dupe existed by overlaying a screenshot over his stream to create the illusion that he duped gold.
The idea that there is some sort of mass duping requires you to believe that over the course of several years (Wrath - MoP at least) that Blizzard was so incompetent that they didn't fix these duping exploits that only worked on specific mounts, gems, and raid mats. If you bought mats that were stolen from someone's hacked account they'd strip the mats from you, that we can verify, but they're so grossly incompetent that they didn't remove these supposed duped mounts / mats / gems. I bought some of these cheap mounts for myself and I bought some of the cheap raid mats for my guild in the relevant times and nothing ever happened. You have to believe that Blizzard is the most disgustingly incompetent people to ever exist and simultaneously that the dupers are the best secret keepers in the entire world because a decade after the first alleged dupes nobody knows how they worked and there's no evidence of them on the internet other than someone's random memories of the time and a widely held belief.
So again if you're just going to provide conjecture instead of actual proof of duping, and engage in Ad hominem because someone doesn't share the same belief that you do without evidence, don't waste everyone's time.
Btw nobody demanded working reproducible duping methods, just any sort of actual proof that they ever existed. This is the internet.
Do you have a timestamp for the bolded part? When he talks about item duping in MMOs he mentions pretty much every MMO except WoW. I could have missed it at some point in the 50 minute video, so if you have a timestamp that would be great, but when they're talking about how dupes work in MMOs in that video they don't talk about WoW. They talk about Conan, FFXIV, Runescape, and a couple others, but not WoW. Thanks for actually linking a video.