It's your business whether or not to use an a real estate professional to represent your best interests but to not do so works to the advantage of the builder in so many ways....
Did you register as not currently working with an agent? Try contacting them and telling them you are considering going with another builder because you feel you need personal representation and that since you didn't bring an agent into this relationship....you feel the need to move on and explore other options.
Jeremy S. Hill, Realtor Associate,
Keller Williams Realty
Licensed PA, NJ
"Your Interest 1st Always"
There is no rule of thumb on how much to ask off a list price. As agents, we base our offers on comparable sales. So, you'll need that information in order to base an offer. Many times builders will not even negotiate on their asking price, or they will give you an "extra" included in the price. A local agent should know what the builder does generally when selling their properties.
Since you've done all the leg work, perhaps a Accredited Buyers Agent would represent you during this process at a reduced commission. Check out http://www.REBAC.net for a Buyers Rep in your area.
Kenneth Verbeyst CRS GRI ABR SRES GREEN