If you have a commitment from the lender, then they cannot just change their mind unless they found something wrong with your application (i.e. undisclosed credits, wrong information on income source, different source of down payment as what was presented initially) . If you do not have a written commitment from the lender and you only have a verbal commitment, it may be difficult to bring them to court. The way we do pre-approval is like getting a real mortgage - submit all relevant documents up front and get the lender give us a mortgage commitment good for x-days. This assumes that your financial condition would be the same or better when the mortgage application with a property is submitted.