Dear Urist McTradesdwarf,
WHY?!?
I offered you 175* over the amount I owed you. Why then did you want to increase it to 350*?!? They're just beer and wine barrels! I only needed something to drink!
Urist McSealdwarf
To Urist McSealdwarf,
Traders are greedy motherlovers, sir. I don't know exactly how sharp they are, but if you don't have a sharp, assertive dwarf, well-skilled in persuasion, negotiation, intimidation, etc, they feel they can take advantage of the dwarf you sent to negotiate with them, and may demand a deal better in their favor, and will get pissed if you keep offering them a deal which is fair by your standards.
To counter this, I recommend, if available, getting the sharpest, most persuasive and skilled liar in the fort to do the negotiating. If you can't, then just have the woodcrafters turn trees into giant spiked balls. Armok knows why, but
everybody considers even babby-tier spiked balls incredibly valuable, and ones of genuine quality (for wooden objects,) will sell like crazy. Maybe they all think giant, spiked wooden balls are a form of avant-garde Dwarven art they can't understand, so they pay a premium for them so as not to appear to be stupid.
If you don't have any time for that, just seize the goods. You can go through a trade depot's menu selectively to Dump the goods you want if they're a Dwarven caravan, or just dump the whole thing (possibly including the traders' personal belongings, if you're feeling vindictive) if you're in a hurried mood.
You can also sell prepared meals for astounding prices, so if you really need to, you can buy whatever food is within your price budget, mince it all up into a roast, sell it back at a ridiculous premium, and buy whatever you like.
I just use the BALLS BALLS BALLS trick, though. By now, I'm half convinced that gargantuan wooden spiked balls
are art, given the quality that my carpenters have been putting out. Thinking of hanging a pair from the walls or something.
Sincerely,
Overseer McFortressBalls