Bright Spark -missives are not offers to purchase, they are conditions of purchase and are not signed by the potential buyer or seller, but their solicitors. Once the missives have been dealt with the potential buyer then puts in a formal offer to buy. Once the offer has been accepted on all points, you have entered into a legally binding arrangement and neither party can withdraw without potentially being held liable for the consequent losses of the other party. This is different from the English way as you can accept an offer at any time, but until Contracts have been exchanged and both parties have signed, you can pull out without penalty.