The app looks good and I tested it a bit. Don't think of it as a way to replace trade, but more to facilitate large trades in the long run. Like on Popham we need thousands of Oiled Boards and Dry Boards etc. So should some large project, you could place buy orders for large quantities. Small quantities would be good too, especially once the graphs are in and you can get a good idea of pricing for things.
I found a teasel and saw people buying for 400s and Heffernan buying for 50s so I didn't know what was what. This would give everyone some idea of a going rate. Having a market system will be... odd for the time period but whatever

I look forward to the logistics needed and the drama which will obviously be tied to all this, in a really good way.
If nothing else, it is nice to see that a gamer who loves running a trader guild has found a home in Salem.