As for the Bonds, the reason is simple. It's a brokerage, the money is all handled by the clerks in the capital. For gameplay reasons, if you broker a deal you shouldn't get the difference in golds but in bonds.
obviously you should never be able to change bonds->gold outside of bank... as i mentioned above.. i don't think the other way is a big deal.
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1 funny thing... i've been sitting on my arse for days in fissoa wondering why the hell there ain't no buying deals from d'hara - my trader's realm .. trader not that high skilled i don't think, with a radius of somewhere between 500-600 miles...
it's too bloody far away (around 700-800 miles away from character).. XD
so in a way it's bad, because it would rule out what i did before, travelling from d'hara to summerdale (which is even further away) as a new trader and bring back a load of food.
perhaps traders could broker deals with other traders (sort of boosting the signal to reach even further) as opposed to just deals between lords?