1. Force majeure (doctrine and case law)
Force majeure is accepted by the administrative doctrine (BOI-ENR-DMTOI-10-50, § 70), which may be relied upon under article L. 80 A of the Tax Procedure Code. Three cumulative conditions: externality (a cause external to the property dealer and its organisation); unforeseeability (at the time the commitment was given); irresistibility (an insurmountable impossibility of selling throughout the entire period). A fall in the market, the absence of a buyer at the hoped-for price or the prospect of a loss do not amount to irresistibility: they make the sale less advantageous, not impossible (Cass. com., 14 sept. 2010, n° 09-15.495; CA Versailles, 24 janv. 2002, n° 1999-2214). The real-estate professional is moreover presumed to have been able to check the planning constraints, which rules out unforeseeability.