Actually got two cars off them so far. r33 which i got in december 2008, took me half an hour to cut them $200 off the advertised price. got my current car from them half a year ago. paid exact price as they advertised, but got immoboliser put in for free. From my exp. you will be lucky to take a few hundred dollars off the price they ask for. As Kezr33 stated, they are a businnes after all.
Paid cash for both cars by the way, which didnt really make any difference on the price.