Involuntary autocorrect in operation on mobile device. Apologies in advance.
networkn:LookingUp: My wife and I once got what we considered a great deal when we were looking at moving. We found a house that we wanted to buy and made an offer contingent on the sale of our current property. We then offered our current property to the same agent (who was quite formidable), and stipulated a rather optimistic minimum price, under which we wouldn't go under any circumstances. That gave the agent incentive for two commissions, she worked very hard on the sale of our house, and actually got us quite a bit more than our preset minimum. I guess this approach only works if you're moving locally, but you may be able to swing something similar if you're moving inter-city.
The flaw in your theory is that a sale which has conditions like this will yield a higher selling price than one without. We got 30K off the price of our current house by removing stuff like and "taking a punt".
30K more than covered the agents fees :)