13. Any sale that is entered on the basic list, has not been subtracted under Subdivision 2 and was made for a price not reasonably corresponding to the actual value of the unit of assessment according to market conditions as of 1 July of the second fiscal period preceding the fiscal period for which the median proportion is being determined shall be excluded from the group of sales that may be used for purposes of determining the median proportion, where the price adjustment prescribed in Subdivision 3 is not expedient or cannot be performed easily and objectively.