Well, if it's anything like the domestic security industries, the quality of the personnel will vary wildy.
A private security firm can be anything from an ex-con with a Van and a mangy old German shepherd dog, to a professional company aimed at guarding at-risk VIPs and comprising a bunch of ex-special forces on its roster (I do know a couple of people who do that incidentally).
But one would imagine the typical average mercenary is probably some ex-squaddie with an AK-47, hanging around Mogadishu with a chip on his shoulder, ready to sign up for any old tin-pot outfit. And let's face it, that's a career path that is definitely going to attract its fair share of nutters and dreamers.
Chock