According to wikipedia, “Gazumping occurs when a seller (especially of property) accepts a verbal offer (a promise to purchase) on the property from one potential buyer, but then accepts a higher offer from someone else.” In simple terms it refers to making a higher offer for a house than the buyer whose offer was already accepted by the seller and thus succeed in acquiring the property. Although this can also intend that the seller raises the asking price or asks for more money at the last minute, after previously verbally agreeing to a lower one.