There are various ways of going through the negotiation process, I have heard a fair amount of success of people using brokers. Personally I hate dealing with any high pressure sales type of thing, so we actually contact the broker that my Wife has access to through her job. In the meantime I sent emails to all the Toyota dealerships within 50 miles.
The funny thing is that within 48 hours I was emailing back and forth with a handful of dealers, mostly playing the prices against each other. I ended up with in a couple hundred above invoice for the packages and color I wanted. The car was in transit to the dealership before the broker even got back to me...go figure.
As far as the emails went, I was very specific as to the options I wanted and the color choice. One or two dealerships said I would have to pay a premium for the color I wanted (Blue Ribbon), most did not. Some came through with a partial list of options or more than I wanted, again I either scratched them off my list or sent them a copy of an email from another dealership that had what I wanted. All in all it was about an hour's worth of emailing back and forth until I went with one dealership.
I was surprised how much easier this was than in person, though still a little stressful.
The biggest downside for me was that they still tried to play games with financing and trade-in. I didn't finance through Toyota so that was easy, just had to keep telling them no and I went in armed with KBB quotes on the trade in, took a small hit on that but I figured I would anyways.
To get back to your question, the broker did eventually get back to me and what he would have been able to do was not too bad, but not quite as good as I ended up with. However, sometimes not having the stress or spending the time negotiating can certainly have some monetary value to off set such a thing and just to reiterate the broker would have been able to get a decent price on the car.