Well it turns out that in many cases that those aren't job postings. They are just looking for free content for other people's web sites and they are getting paid for your sample articles.
Have a look at this message board:
"Heyya peeps, haven't been on in a long while since the hack attacks, but got into this AC thing. So far its shit cause they're real big bloody assholes about what kind of articles they want; kinda like a little kid who picks at his food.Remember that if it seems too good to be true it probably is. Be especially wary of job sites that don't charge for posting (Craigslist in particular is primarily a spam board now.) Do not apply for jobs unless there is a legitimate company attached to it. Even if it is through an employment agency they should have a website somewhere that you can look at.
Well I guessed they couldnt turn professionally written articles down so here's what I did short and simple. I went to craiglist put up a job listing in suburbs and shit like that (since the cities cost $25), it was for a writing position on how-to's and guides. I instructed them to send me a newly written sample 500 word article on a topic that I chose for each ad. I also asked for a resume to make it look more authentic.
Took about 4 days, but I got maybe 10 to 20 articles on good subjects that I submitted to AC and got paid a good $35 bucks total for the articles since they were very nicely written.
Try it out and enjoy!"
Don't give them anything, not even a resume (which could aid in identity theft), if you don't know who they are.