From experience, these people hired farmers (people who take money and then hire some $1/article junk writer) or the writer plagiarized their portfolio and bid and the client got something off-the-wall bad but just paid the writer anyway.
A lot of offshores writers completely plagiarize samples and their bids, so the client has no idea unless they make a phone call or email back and forth. Of course, you can spoof your location on Elance, so it looks like they are in the US or Canada. I combat this by only giving references where my name is on the article.
With the farmers, they will charge cheap (like $10/article) and then hire a junk writer, so the client has no idea that they are getting third-party junk until they get it.
I used to hire for a company that gets posted to this place a lot. lol One of the farmers I compete against on Elance gave us completely plagiarized material and he was on our blacklist. Farmers are also the guys who claim to have "teams" of writers. These "teams" are usually from third world countries where the farmer takes most of the cash and then hires the junk writers. They always tell you that the writers are from the US, though.
The best writers you can get are ones who work individually, know your topic, and they are responsive to communication. That doesn't mean Skype either. Skype is a time sink and I avoid it. A lot of my customers who have big projects want to have a conversation with me, because just hearing a voice and personality helps you decide. A good writer should have some communication with you, and you'll instantly know if they plagiarized their bid and portfolio samples.