D owned 12.75 acres bordering the Sudbury River. A statute authorized the Commissioner of Natural Resources to acquire approximately 1,000 acres of the marsh and land along the river as lay 'at or below the [120-foot] contour interval above mean sea level,' unless the owner preempted the possible taking by subjecting the land to a conservation restriction. D chose the preemption alternative and executed an agreement with the Lincoln land conservation trust restricting the wetland portion of their property to uses, which would preserve it in its natural state. D entered into a purchase and sale agreement with P to sell for $400,000 their land and a single-family house on it. Under the agreement, D promised to convey 'a good and clear record and marketable title,' free from encumbrances except for those specifically noted in the agreement. The specified encumbrances did not include a restrictive agreement with the Lincoln land conservation trust. P declined to take a conveyance subject to the restrictive agreement and demanded return of her $40,000 deposit. D refused to return the deposit. P's motion for summary judgment was allowed and D, the sellers, have appealed.