It is legal, but IF the purchase is contingent on getting a mortgage, then you won't be able to sell the home--the buyer can't get a mortgage if the home won't appraise (and the lender cannot be made to lend if the home doesn't appraise; the lender is not a party to the contract and is not bound by it). If there is also a finance contingency in the contract, then the buyers would be released from their obligation(s) without penalty if they can't get financing. Of course, for a cash sale, the appraisal is irrelevant if the buyer agrees to not have it affect the price.