C'mon, while there are undoubtely difficult properties to appraise, let's not pretend for one second that the typical 1,500 sf dogbox on a 7,000 sf suburban parcel area is difficult to appraise in most areas so long as you have access to the needed data sources. Even if you have locational issues, such as the subject property being location on a busy road, etc., so long as you have access to the needed data sources, it is not terribly difficult to determine the effect of the external obsolescence on value.