It was shown on Dutch TV recently that a company set up in NL doing this, has seen their turnover going through the roof. There are a lot of people who hate haggling, but still like to save money. It's a great idea imho.
There's a company near me who basically do that. You give them details of the car you want (new or hardly used) and they then find a car and negotiate a good deal on it.
A chap I know got a 58 ML320cdi (15k miles) for £22k from them.