Im afraid I have heard about the exact same thing. A friend of mine usually advertises his rides over here, and told me that even before his ad got posted, he received calls with offers for his ride.
This is pretty abd, though truth be told, the same happens when you submit an advertisement in any newspapers, they usually get leaked the day before.
JUts makes you wonder as to how may cars have been picked up at a bargain, because they never got their ad placed!