It seems like every time I pull a diamond player/equipment and go to sell on the market I am immediately under bid. And within a few hours that price has dropped by thousands of stubs. So when I pull that said diamond is it because that particular diamond is pushed out to everyone? It doesn't really seem plausible that a bunch of people already had said diamond in their inventory and just happened to try and sell it when I did.
No, people are manipulating the market. If you own 100 of the same item, you can wait for people (like you) to put in a sell order and then put in a ton of lower sell orders to make it seem like the market crashed. Then they can buy even more inventory at the lower price. They are actually targeting small time flippers who often buy at a artificially inflated price from one of these whale's sell orders, then are stuck unable to sell at a profit when the whale flood the market with stuff he bough at 4k stubs less than the small timer.
At least some users are using robotic process automation tool to scrape the show website, capture the lowest sell order, then underbid by 1 stub. This can all happen in a couple seconds, with no user intervention. Can be set up by anyone that understands this stuff within a few minutes. It would be laughable to suggest this is not happening, and captcha does not reliably prevent it.
I have no idea about the automation part posted above, but do you open packs in the early evening or other times when lots of other might also be opening packs? That could be part of it. Outside of that, I’ve got nothing.