The appraiser does not work for you. The appraiser works for the bank. The bank is not liable for repairs on your home. The home inspector and your real estate agent work with you to protect you from houses that have issues like this one. Your agent can bring the other agent together and if they are Realtor members they both agree automatically to go to mediation. During mediation, you will describe that the property was not disclosed honestly and the septic needed repair. Then the person who actually cheated you can pay for it and if the agent knew, they are liable. Regarding an error on the appraisal, the disclosure was not on the contract, because obviously it is evidence that they did not disclose this problem. GO TO YOUR AGENT AND SELLER, we have nothing to do with it other than if you default on your loan that was over valued appraised. This is called damages, but if you pay your mortgage, there is no loss to the bank. If somehow you made the grave mistake of not having representation, you may have to sue them to recover your loss. Look on the contract, does it say Realtor? If it does you can get your money without going to court. Did the contract say "as is?"