Yes, been around forever. Free market. No way to stop people doing it without controlling the prices like Black Desert does (which I would prefer WoW copies, tbh).
Now that you know, don’t just undercut without looking or use an addon that makes sure outliers are noticed.
The AH has been unified for many or all realms, so there is very high activity all the time, especially on mass-traded items.
People post autosell lures and then buy them off once some numbers have accumulated. It might also be other people than the lister who want to foil their scheme, and if you do that, you can actually see it stop quickly, because they seem to notice that someone else keeps buying their lures away.
You get the message that you cannot buy those items because the list is outdated because someone else has already bought the stack.
Also be aware that there is no listing blocking or whatever you tried to explain. The system was changed to LIFO (last-in-first-out) for sell offers of same price. It is arguable whether that is a better or worse system and was officially done to prevent excessive undercutting, but as so very often I think we can agree that Blizzard could design various systems much more logically intelligent.
And this is not a scam but a market manipulation, and don’t expect Blizzard to stop this behavior, so you have to get used to spending the little precious moments to look at the list on the right and decide whether the lowest listing - if you want to sell at that - is a legit one or not. - In the extreme case of 1-silver listings it is even easy because you only have to look whether the suggested sell price is 1 silver.
We should disuss why people aren’t complaining more often about the quantity field for buying stuff having the tendency to not mark the default “1” but sometimes does.
The 1 stack that gets posted is not buyable and remains for a considerable amount of time. Any other stack on top of it to that price gets sniped in <1 sec. Its a bug and being abused. They probably buy the 1 stack instantly with a twink and disonnected during the process so the item is in a loop and cannot be removed in any way. Now the auto sell price is set at that item until the timer runs out and the item gets removed.