I saw a video on YouTube a while back. It was about making money by using Ebay and Craigslist. The video was simply a guy explaining how he checks out Ebay to see what is selling and the selling price. He then goes to Craigslist and tries to find that item for a little less than what comparable items are selling for on Ebay. He buys the item and immediately starts an auction on Ebay to sell it. He says he only makes a few bucks on each item, but repeating that process over and over can build into some serious money. That could work, but I have my doubts that it would work consistently, and I doubt that it will work much longer, especially because he is giving his "secret" away.
There is a similar routine being used by recruiters, if you ask me. I am pretty sure that recruiters are out surfing the job posting websites just like we do. These recruiters can be located anywhere in the world, even in India. After all, it is the world wide web.
The recruiters find a posting and then go to the posted résumés on Monster.com, CareerBuilder.com, etc., and look for résumés that sound like a good match for the job posting they have found. They then contact the person that posted the résumé and, for all that person knows, that recruiter was given the job by the company posting the ad. If the person seems interested, the recruiter contacts the company that posted the ad and probably says something like "have I got a candidate for you". The reason they do this is to get a finder's fee, a bounty of sorts. I don't think that is illegal, but I would think it subtracts from what the company might be willing to pay you if you had answered that ad directly. And it could have a long term impact if you end up actually working for the agency that told you about the job, if they become your agent. They will end up taking a cut of every paycheck you get.
Have you ever noticed that you tend to see the same job listed several different ways, by several different recruiting agencies? I think they must grab the original ad and run it as their own. I don't know if that is legal to do without the original job poster's permission. I am sure some companies turn their recruiting over to agencies once they have given it a try and not had any luck.
I suppose the point is: know what you are getting into when you accept an offer from someone other than the actual company offering the job. I think it is fairly common for recruiting agencies, especially if they are located in India, New York, or California, to just get a finder's fee and you become a contractor for the company offering the job.
If it is truly a contract job that is not going to lead to a permanent position, the company may not want to deal with contractors directly. They may have a policy of only using contractors that come to them through a company that supplies contractors. That was how my last contract worked. I was actually employed by an outsourcing company that, for the most part, exists to supply contractors to the company at which I actually worked. I was an employee of the outsourcing company with subsidized health insurance coverage, paid days off, and paid holidays. However, I was expected to work 40 hours a week.
When I see ads that look like they have been taken from some other original ad, I do a little research to see if I can find the original ad. The original ad may have been taken off the job posting website long ago, but the recruiter may still be running it for bait. After all, it was once a real job, and probably sounds pretty authentic. If you apply for the job, they get a copy of your résumé, which they can file away, even if it is not posted somewhere. Of course, that is not all bad. They could offer you the next job they see, which you may not see.
If I find the original ad, I can apply directly to the company that has the job opening, unless they do not want to deal with contractors directly. I think I have a better shot at getting a job if a recruiter is not in the middle of the transaction trying to get a fee for offering me a job that was already directly available. You might check the company's website Career area and find out the job is no longer available. Or the company offering the job may not trust the agency that contacts them with your résumé, which would put you out of the running altogether.
As I said, working through a reputable agency has its advantages. I would just suggest checking any agency that offers you a job. Do a little research on them. Check their website. Scan for their name and the word SCAM. You will most likely get a sense of whether they are legitimate without much effort.