You have no basis for suing the consumer for cancelling the mortgage loan: that was his legal right to do so, even if the decision was unwise or inexplicable. People are not liable (that is, may not be sued over) actions which they are legally entitled to do, even if those actions have negative consequences for a vendor, sales rep, etc. If you are out of pocket, that is not legally the customer's problem: it is a function of the fact that when you are a business person, you often have to invest in or spend money on potential sales that do not come to fruition; that is the cost of being in business.