It will deepend what your sales contract states. If the sale was cintingent on the buyer getting a mortgage, then they were declined becuase the appraisal was too low, then yes you have to give it back. Of course it depends on if they were within the dates of the contract and if they gave you written proof. If you are unsure, you should have a lawyer review your contract and everything the buyer sent you. The easy part of most sales is finding a buyer, the hard part is getting it to close.