To be clear, they’re not being “banned”, just locked. And it’s due to a huge issue that came up with the AH after the latest patch where cancelled auctions would later send the player an amount of gold anyway.
It’s been patched, but Blizz is still working on fixing the damage done…ie. removing the gold from people this happened to.
That said, I don’t know if Blizz will action any accounts that took advantage of this bug or not. Only time will tell. But right now, all we’ve heard is that some accounts are “locked”, not banned (complete closure of an account).