I tried
www.betterdeal.com.au in November last year but they told me that the Qld Dealers were not able to participate in betterdeal (at least on a 335) so I should consider involving NSW dealers. Only got 1-2 bids and they had only bettered the starting price by about $200. After the auction betterdeal said there were dealers prepared to offer me a bit more discount but they didn't want to participate in the betterdeal auction because "BMW were not discounting 335i" Anyway ended up negotiating with a Qld dealer myself.