Definitions for "Gazump"
Raise the price of something after agreeing on a lower price. Usually used in association with real estate market, means that the seller raises the price of a house and in response to a better offer - just before the deal is clinched. It is unethical but not illegal.
rip off; ask an unreasonable price
Gazumping is when a seller pulls out of an agreed sale after accepting a higher offer. This may result in the buyer losing money spent on things such as building surveys.