With in game automatic trade system and without APIs you may have more control of trade, it really is harder to wrote application what's going to exploit in game trade system, actual much simpler is using browser scripts (at the particular state, sites like poe.trade you never even should wrote anything it s already done).
So why is bigger gap, internet websites (with integrated notification to Buy POE Orbs system) and applications with by using same exploiting trade API maybe in-game controlled trade system?
In my everyone hates on getting an real-time Auction House simply because they had seen the Cheap POE Items way it can fail on a lot of other games untill today, but that doesnt mean you only have copying the mistakes other game have inked.