I just had quite the epic battle go down outside my fortress. A cyclops arrived, ready to raise hell in my fortress for no other reason than it being there. After my inital reaction, I changed my pants and then sent my militia commander at him. He had a name, a steel shield, and a steel mace, but little experience with shield or mace, and his name came only from murdering elf merchants. Still I was hopeful one of those rare miracles would happen, and my militia commander would manage to bring it down.
He failed completely, only inflicting superficial bruises before dying. The Cyclops wasted no time pursuing the other dwarves, this time weilding his fallen foe's steel shield! He killed a herbalist a pursued others, who were blinded by panic and stupidity and didn't think to draw the creature into the weapon traps. It was starting to look like another poor fool was going to die, but suddenly, a challenger appeared: A human swordswoman, who was just leaving with the merchants. She checked the time, decided she could stick around long enough to kick some ass, and leapt at the monster, who was distracted with beating another herbalist. She announced her presence by stabbing him in the arm, then chopped his eyelid off!
The cyclops, wide-eyed due to fear as well as the loss of aforementioned eyelid, decided he was done for the day and fled. The human followed him, stabbing him whenever she got close enough, so that the cyclops's path was marked by his blood. Several times he turned to fight back, but quickly changed his mind when he saw he was just pissing her off. When he finally collapsed due to having shed copious amounts of blood and presumably even greater amounts of fear urine, the human hacked his skull to pieces, seemingly deliberately avoiding the brain so as to prolong the beast's suffering.
When the cyclops finally died, gladly arriving in Hell because the psychotic swordswoman was not there, the hero who had saved presumably many lives left. She didn't say goodbye, apolagize for the mess, or stop for a breath. She simply walked off the map, knowing her work was done.
And that's why I don't mess with the human merchants.