At this point, I'd just say to put relisting/trade cooldowns based on the level of the item. The closer it gets to max level, the longer you have to wait before you can adjust price/relist. It won't eliminate undercutting, but it will stop bots from constantly shaving a few gil off every few minutes unless they're massively overstocked. At which point, I'd argue it becomes even easier to identify them if routine scans find x of the same item on cooldown despite having multiples listed.

FFXI-style AH wasn't any better and prone to its own exploits, imo.

End of the day, player-run economies in games tend to fail precisely because of bad actors, where you either have to join in on the cheating or suffer through its effects as a more casual player. I'm kinda nearing the point where I'd just prefer solely interacting with NPCs, selling and buying things at nominal prices instead of dealing with the proper time of the day/week to sell things, hopping servers because mine is backwater on value, etc.. Major patches/expansions only temporarily reset that sort of decay, which on its own, doesn't address the bot problem that, given the age of this thread, seems to be half a year strong now.