I was also wondering what was in this for the scammer. There was an article in this weekend's Denver Post that explained this.
A scammer, often in the scammer haven of west Africa, copies your pictures and puts up an ad for a rental. They say they had to transfer suddenly, and the place is now for rent. The rent is below market. When you, as a potential tenant, contact them, you find out they are in Africa, and have the keys. They will send these to you so you can check it out. But wait, who the heck are you, wanting the keys to my house? You need to send me a deposit of $1500, wired to my bank in Africa, THEN I'll send you the keys.
That's the last you'll ever see of that $1500.