When a home buyer is obtaining a mortgage to purchase a home, then the home will have to be appraised. What that means is the appraisal is ordered by the lender, and they will come out to view the home, measure the home, and will compare it to like properties in the area to determine the appraised price. There are reasons a home may not appraise.
Some reasons include if the property is overpriced, there is obvious deferred maintenance, lot adjustments and more.