The mercenaries around Vehl and Hempstead, there are adventurers, both good an evil, killing them. Instead of just killing the underlings wouldn't it a good idea to go through the chain of command and kill the head honcho? There would probably be three ways to kill him(or at least that's all I can think of); one you could talk to the right people and build your prestige amongst mercenaries and get led to the all mighty owner of the group. Two you could interrigate a less than loyal mercenary who might give you the right information. Three the good old guard in Hempstead have been doing some investigation and they have a mole on the inside of the ranks of mercenaries who gets a group of good and strong adventurers into the works and they can get the job done. Now I know that the low level mercenaries are an easy way for low level charaters to band together and do something in the difficult world, and if you kill the leadership of the mercenaries the whole mercenary thing could fall apart. However there are poor people who are still desperate to go great lengths to earn a living, and they could just as easily become a small group of peasant friends who decide banditry is the way to go.
Another little idea, if this is done by evil people, couldn't they join the mercenaries instead of kill them. Then it could lead to an shady, underground guild who is more fond of the highest bidder than the goodness of people.