Having just gone through the process, here is what I did.
I found out what I exactly wanted and hit all three with it. I did make changes along the way, asking each dealer to do a bit of research so that no single dealer was answering all my questions. I verified all answers from the factory as some dealers are not all that good with product knowledge (go figure). When I talked to the three, I let them know that I was shopping, but refused to name any dealers by name at this point. This was basically round one. Being the customer you have the power, a good dealer will not take shopping personally. A good dealer/salesperson will show why they are the best. If they do take things personally, it’s a pretty good sign that the dealer and/or salesperson may have issues. There is nothing unethical about shopping at all. You hold the cards as the customer and as long as you keep it above board you will have played the game well.
Round two is where the highest ones started to fall off the scope when I asked if they would be interested in matching or beating prices. At this point, having the info in hand in the form of an emailed or faxed sales quote was helpful. I did mention dealers by name at this phase and when speaking to the dealers made it clear that the info was in hand and I would be willing to share it with them. It's kind of like playing poker at this stage. You can bluff a bit and maybe not get called on it...or get called and loose face a bit and possibly have to move to a different dealer. I honestly did bluff a bit, but not much and was not called on it. I did ask that the pot be sweetened and the winning dealer seemed more than willing to dance.
It then came down to two and as I've PMd you, the one pretty much shot himself in the foot.
There are peddlers and there are sales people. The sales person will never talk smack about other dealers. They will offer you a price and negotiate in good faith as is part of the process. When a dealer starts to talk smack like "You know those dealers that low ball might not be in business long...." you should run, not walk as more times than not when I've come across this mentality, it's almost always been a bad sign.
Remember, you owe the dealer nothing. It's the dealer's job to meet your needs not the other way around. You are the consumer and as such it's not your job to sell, its theirs.
On the old coach I got about 17%. On the new one, including trade differences that the dealer met, I got about 12%.