Actually, these places have deals with "approved agents" that the agent will give them a 30% referral for giving them qualified leads. Out of this 30% they give a rebate of some small amount.
Honestly, you are better off talking to the agent ahead of time and saying, "I could go through program ABC, but maybe you could just give me a rebate yourself." They probably can't give you a check directly, but can give you a client gift which could be Best Buy GCs or something similar.

ziprealty.com gives you 20% of THEIR comission.

You get the 1% regardless of whether or not you bring an agent with you....

My wife and I are building a house currently (builder wasn't on inest and I didn't learn about inest until after the fact anyway....) and we're bringing an agent with us next time. We'll never do it without one again. We've had so many problems because the builder views us as people she can roll over because we don't appear have anyone looking out for our best interests.

the max commssion they get is 3% of the sale price. so the max you can get back is 0.6% of the sale price. this will work better than inest if you have a lot of options added to your house.

remember, with inest you get 1% of the base price of the house, not the total sale price.