3) greatly reduced availability of trades for lords. I can think of two things off-hand. First, restrict lords to trading with adjacent regions only. Second, make newly posted orders visible only to traders for the first three days after they are posted. Lords can only see them once they are 4 or more days old. This allows the traders to get an exclusive shot at all new offers before lords can act on them.
I like this. It makes traders especially important when food is scarce, and needs to come in quickly.
The other option I am thinking about is related to food rot. Right now, food on the market doesn't rot, but it should. I would have the rot reduced considerably for deals brokers (not completed!) by traders - that way pure traders doing the trading game profit from this, but region lords who become traders to game the system don't.
And finally, yes a posting fee for non-traders. The logic being that only traders can access the market, and region lords can it, too, but have to pay some NPC trader to act as a go-between. Those fees would be flat per-deal ones, and much less for posting than for completing. Say 5 gold to post an offer, 10 gold to complete a deal. It's not huge game-changing unfair, but it's enough that over time it matters. A rural region constantly selling its surplus will feel it if every deal costs 10 gold.
