Madina always was the least interesting trading partner because it was by far the most expensive.
Hey! I find that a completely insulting! Fatmilak's prices are reasonable
But in all seriousness, I've never had a D'Haran Lord even try to barter with Halicos. Vallyn does it all the time, Abbot had a bit of a go at it and a few other Madinans have done it in the past too. He had 2000 bushels sitting in the region dying to be bought, I'm pretty sure he even told you (or some D'Haran Lord) that and nobody bothered to say "well, I could buy the lot for 30 gold". He'd have jumped at that (well, maybe he'd have haggled a little) just to get rid of the damn stuff.
Chénier, remember that you control the prizes when your wharehouses are full. 
The simple rule of supply and demand.
Not overly. There are quite a few other places to sell food, it's just D'Hara is the easiest. He probably has more bartering power than anyone else because it's easy to sell to him. If he pushes too far, we'll just move elsewhere. It takes a little longer to sell our food elsewhere, but it can be done.
