To the illustrious Kaspa, Overseer:
My good sir,
It may surprise you to know, that the added expense deals with a number of extenuating circumstances, and has very little to do with any personal predjudice, I assure you.
In the instance of those fine iron bars, one must consider what is required for them to be offered from amongst my fine selection of wares. A prospector, to identify the ore deposit, miners, to reveal the ore and free it from the cold earth, haulers to move the ore to the stockpiles and foundries, a foundry worker to smelt the ore into quality metal, an animal trainer to train my pack animals, a carpenter to construct my wagon, and of course, where I come in at the very last, the merchant, who makes the journey to present you with such fine merchandise.
Clearly, one can see how each one of those steps must invariably add value to the cost of a product, how a coarse wooden barrel and a featureless, drab, burlap bag filled with simple seeds just isn't sufficient for barter? Perhaps if one had encrusted a high quality barrel of fine craftsmanship with traces of lustrous metals and brilliantly sparkling gems, and if one had presented such seeds in a beautifully embroidered bag of excellent workmanship, could have had a deal, but as it stands with the merchandise such as it is, I simply can't imagine you getting all those items you wanted to trade for.
Clearly, if I am to be able to continue being a merchant I must return with items of sufficient value to cover my initial outlay, and the expenses of the trip with some extra. If I traded at a loss, my business and liklihood would surely suffer for it, and so I simply could not do that trade.
I look forward to seeing the amazing crafts and products of your impressive contribution to our glorious dwarven kingdom next autumn when I return, so that we might engage in a mutually beneficial enterprise.
Afterall, our fortunes rise and fall together!
Urist McMerchant.