Make the contract subject to the loan amount you need to do the deal. If it does not appraise out then you can not get the loan dollar amount you need. How much earnest money do you have to put up? This is really your only thing at risk. If the house does not appraise for what you need you can just walk away and lose the earnest money or even agree to split it with the seller. I do not actually reccommend this but it is one way that the system works. You could get the reputation for tying up property and not being able to close. You always want to close what you have under contract.