M & S is not the final word. The local building cost should be. The fact is market conditions dictate whether the market will pay more or less than cost. In a falling market, its more likely that cost will exceed sales unless you use a negative Enterprenuerial Profit factor...which cost books don't include (out of practical considerations that are wholly sane to me.) In rising markets, the cost appraisal will lag sales despite EP - because builders are raising margins according to demand. E. P. is another fantasy that muddies the appraisal sciences into the swamp of fable and voodoo. There is, without a doubt , more bad cost approach information than any other aspect of appraising.