Depends where the property is. England, Wales, Northern Ireland, yes, you can withdraw the offer before exchange. Scotland has different rules having a different legal system with offer and acceptance being more tightly defined. Other places may have penalties payable if you retract the offer (France does), but we are astonishingly lax and it costs innocent sellers a lot of time, money and frustration, while intending buyers may 'intend' on several properties at the same time and not buy any, and all that with impunity.