After 8 years both the app version and the web version of the AH were finally closed.
A Blizzard CM actually commented and said one of the main factors for closing it besides how few people used it was because of exploits related to it.
Source: https://us.battle.net/forums/en/wow/...page=3#post-41Basically this. The Web/Mobile Auction had a lot more issues with keeping it up than it was really worth for the small amount of players that actually used it. Trying to tackle and fix those issues (for transparency the majority were just exploits) just takes dev time away from working on new content. While it may change in the future, we currently at this time aren't planning to bring this back.
So I'm curious, how far did these exploits go. What crazy stuff could be done?