Actually we can send a trader from city A to an hub and gain visibility over it.
But visibility is only granted to city from where we sent the trader.
Also it is not possible to trade directly from another city to the hub, even if we have a trader there (from another city).
Moving goods from and to hubs is also very very hard. You have to send vans to the hubs, then command bunch of them to move items. Moving items from an hub to another is a mess, and even if you can buy multiple traders, thinking to have them on more than 2-3 hubs, is practically not that useful.
I think trading will never fly with all those trouble. It hasn't and we are ? two months from release?
Proposal:
1. Once we have a trader in an hub, we should be able to see that hub, from all cities, and we should be able to directly trade with it from any of our cities. We should be able to partially fill any hub orders in that hub from any city, directly or by the hub.
2. Once we have traders in more than one hub, we should be able to move goods from one hub to others WITHOUT use of our own vans. May be for a fee, we should be able to order movement of goodies from one hub to another, at very fast speed, and with fully safety. Personal vans should only be needed to send or receive items from/to hubs to/from cities.
May be other adjustment will be needed, but those two I think are essential to shake the market and revive it. Local markets are now too much trouble to manage, and even when you see something to sell, probably you have the item in another hub.
Removing the global city order visibility could help, or hit the market for the total death.