How can the same home be listed twice on zillow?

A friend of mine has just fallen victim to a scam.  A listing on your site showing a home that met their needs popped up and they requested contact.  She was called the next day by the supposed homeowner and told the details.  Once she had made an arrangement to recieve the lease and keys to the property she sent a moneygram for the deposit and all seemed well.  They stopped by the property to look around and found the owner inside.  The owner went on to tell them that the name of the man they had spoken with was the same one who sold her the house and that he lived just down the street.  After a short conversation with the man renting the house no other address was revealed and it was already too late for her to withdraw the moneygram that had been sent. Through a simple google search they were able to find the home under the name of the man they'd believed to have been speaking with, Jeffrey Young.
When they went to the other address listed for Mr. Young they were able to speak with the actual Jeffrey Young who had at one point owned to original home in question and the one he currently resided in.  No contacted has been established with the gentleman that they spoke to.  When trying to show the listing to me on your site we only found the one listed to the current home owner and were unable to view the one she had been looking at as a rental but upon closer inspection said that the ad she saw was exactly the same as the one showing for sale, pictures, blurb and all excepting the estate rep. How can the exact same advert for the exact same address, representing the exact same property be posted on your site from two seperate sources?