Some may negotiate, some may not. Never hurts to ask. If you are going to try, you should also expect to make a commitment if the dealer is able to work something out that is agreeable to you. There's no set percentage, it depends on the dealers overhead as far as what he is willing to do.

+1

Very good feedback Sky.

I would ad that some selling models require that you negotiate or you will over pay for a window by nearly 2X fold.

Thanks for the advice. After reading some of the Window topics, I think I can guess which type of offer is more likely to be negotiable. My plan is to narrow it down to two or three offers, and then politely ask them if that is the best they can do.

A patient homeowner gets a good price. Just don't be tricked by a too-low price. I think it is most important to determine exactly how the windows will be installed versus price per window. One leads to clear expectations and the other sometimes to cutting corners.

don't make the common mistake of giving the work to the lowest bidder, you could be setting yourself up for a very expensive mistake. far to often home owners think they are great businessman/negotiators and wind up getting stung due to poor craftsmanship as well as low quality materials. is that being a good negotiator? of course not.
why not choose the company that uses the best quality materials and uses the best install methods. price is a factor but not nearly as important as the aforementioned.

I don't think it is expected to make a commitment just because a dealer reworked his numbers. All bids should be apples to apples as far as methods and installation goes. I would not be afraid of a low bid if you have done your homework and you are comfortable with your installer/dealer.

keep in mind buying windows is not akin to going to a used car lot where you can chew a guy down. professional contractors usually use higher quality materials and expert installers. these factors in conjuction with specific overhead expenses play a large part in pricing. my price is usually my final price and negotiating usually implies that i was not being truthful about the initial quote unless its a minimal amount.
contractors have bills, families,ect...
dont be shocked if a quality installer walks away if you try to chew him down too much. in our business that can be a red flag which usually means run from the customer and move on.