26 U.S.C. § 6695A: Substantial and gross valuation misstatements attributable to incorrect appraisals

a person prepares an appraisal of the value of property and such person knows, or reasonably should have known, that the appraisal would be used in connection with a return or a claim for refund, and the claimed value of the property on a return or claim for refund which is based on such appraisal results in a substantial valuation misstatement under chapter 1 (within the meaning of section 6662(e)), a substantial estate or gift tax valuation understatement (within the meaning of section 6662(g)), or a gross valuation misstatement (within the meaning of section 6662(h)), with respect to such property, 10 percent of the amount of the underpayment (as defined in section 6664(a)) attributable to the misstatement described in subsection (a)(2), or $1,000, or 125 percent of the gross income received by the person described in subsection (a)(1) from the preparation of the appraisal. No penalty shall be imposed under subsection (a) if the person establishes to the satisfaction of the Secretary that the value established in the appraisal was more likely than not the proper value.