@CB yes, that is assuming Barter and buy-orders will be an option, which I certainly hope to be the case. That is a nice risk-scenario that you describe there. :)
Simple buying low and selling high in a town of which you know always has need of certain items, is bit less risky. I think there will be all sorts of subtleties to trading in PFO and the trick is to find something that makes money, if only temporary. At the lowest level there is the simple fact that some settlements will always have more ore, while others will have more food. Many different contenders will try to earn coin with that, in many different ways. This is what makes PFO so exiting imo.
Yes, the thing I describe is open for anyone who is willing to place Alts. I do think that keeping track of a few lucrative markets in real-time (i.e. while browsing the market itself) and also having the means (courier alts)at hand to act upon a good buy and transport the items right away is where you can make coin.
I would expect that the prices on such an out of game website would have a serious delay, unless they use software that is directly sniffing out anything that an Alt is browsing on some market. Maybe it could be done legally, all clientside: but I wonder if it is possible to have 230+ Alts browsing 230+ markets and feed the info they are gleaning from browsing directly into a database that can be viewed on a website.
If that can be done, then I will most likely be browsing that website, and not so much the local markets. You'd still need the network of alts and couriers to get the deals done, off course.
It could get real sophisticated if that website would offer projections on good deals and such; most lucrative runs. Maybe even with the possibility to enter variables like max-length of a run, alignments of cities, /hide closed cities, war-states. However that sounds like an extremely complicated piece of software. And you would still have to make your own risk-calculations based on your knowledge of current affairs in the settlements that you trade in. If you know bandits are in the area, you better hold off, that sort of thing.
I think we will see all sorts of "tiers" of transporting. Who knows, a person running criss-cross across the land may be succesfull in certain instances, other times a well guarded caravan will do the trick.
I would also expect a Harvester who found something nice, to immediately run his own stuff to the second next settlement if he knew it would fetch a better price there then in his hometown. This includes risk, and the settlement would have to friendly: all variable that come into play.