What annoys me lately is how even regular players have addons that can search out market niches or automatically undercut all their listed items by 1 gil. I've come across players on discords discussing how it's a thing and not even uncommon either.
It feels a bit annoying to play legitimately, manually repricing every item one by one, then someone comes along 10 minutes later and undercuts the entire lot at a click while sending out their Quick Ventures. It's a punishment for following the ToS.