I haven't tried playing since the initial version so maybe things are different now, but there's a serious problem where automated traders only consider supply, not demand, when making purchasing decisions. Say you have a city that produces loads of fish. The traders see cheap fish and buy it in abundance to sell elsewhere. Those places load up on fish faster than they can consume it, crashing the price of fish locally. Yet the traders keep buying fish because its cheap at the place that produces it, completely ignoring how the price has crashed at all the other cities along the route. Now you have traders that have mostly filled up on fish that they just carry around, meaning they move lesser amounts of useful product. Not only does it cut into your profit, it also means the traders will be slower at correcting oversupply (i.e. the trader operating out of the second city should be moving the excess fish further inland, but they're filled up with some other junk product they can't sell).
The only way out of this is to micromanage the traders, manually checking the next city or two on their route to see what the prices are like, and using that information to manually make smart purchasing choices. This gets tedious once you have a few routes operating, particularly since you'll need to move a scout ahead of the trader to lift the fog of war for routes to foreign cities.
I've been reading patch notes to see if they make the trading AI any smarter, but it seems they've opted to try to make micromanagement less tedious instead. And seeing as their first major update expanded the military side of the game, I don't have my hopes up that the developers see the current supply-only system as problematic.
That said, if you don't mind serious inefficiencies in your trade routes (inefficiencies that also afflict the AI opponents, fortunately), this probably won't concern you. And in any case, there's a lot less griping about the game on the Steam discussion than there was previously (though there's also less discussion there in absolute terms as well).