If your agent has a sole agency agreement he is entitled to ask for a fee to cover his expenses. Even if you discreetly take it off their books they will still look at the selling history to see if they have been treated unfairly. If done throught the builders agent You could negotiate a nil fee or greatly reduced on the basis that they have not had to do anything and in any case enables the deal to proceed. BTW it is customary for the builder to pay a reduced price (90%?) as he is taking on the risk of selling your house.