Unlike goods in a shop at a fixed price, a house is worth what someone is willing to pay Mamboitaliano Unlike goods in a shop, the sale is not completed on the spot. Unlike goods in a shop, houses cannot be returned within 30 days; all the checks need to be done, adjustments to terms made, or the sale withdrawn from, before purchase.
With houses, either side can withdraw at any point before completion, if the terms of the sale are no longer favourable - no longer appear fair - to them.
None of us can see into the future. No-one can know that a better offer is going to be made a week later.
The point at which you have an obligation to the other side is when contracts have been exchanged. A seller might feel some degree of moral obligation after the buyer has paid for a survey and searches - yet, many buyers pull out at this stage. They, rightly, do not feel any moral obligation to go through with a purchase that they no longer believe is in their best interests. Many sellers effectively withdraw at this point by refusing to adjust the price to take account of issues raised by a survey.
What is a 'fair price' for a particular house, is not agreed until the point of exchange.
The whole house-buying process is a dance, a negotiation. Up until the point of exchange and even, with penalites, completion.