It all depends where the starting price is. If it is way overpriced, sure, you 'should' be able to talk them down a bit, but if it is priced 'right' from the start they are looking for a fast sale and will not haggle knowing it is worth what it is listed for. Then the whole supply and demand aspect comes into play. When I was looking for a used 4th (right before the 5ths came out), I found exactly what I wanted. It was an 08' Limited lower miles, fully loaded, the color I wanted (I did not let them know it was the perfect match). It was way overpriced and they would not deal at all. They acted like they had the only one in the country and if you wanted it you were going to pay their asking price (which if it was fair I would have). Oh well, their loss, I bought a new one from another dealer.
I have 3 dealers in my area...when I saw the 5th released I told them what I was looking for and asked them to call me when ANY model came in so I could take a look. One dealer called with the exact one I wanted, good deal and done. I got a call almost a year later from the other dealer and I just laughed, never heard from the 3rd. So, all depends on how bad they want your $$$>.