Appraising 4 Units - Cap Rates

[Stefanie Campbell]

When dealing with an appraisal on a 4-unit, that you feel has been significantly undervalued based off the comps the appraiser pulled. What is the best way to challenge the appraisal? I'm assuming by using the cap rate to determine the value instead of the comps alone? When determining the cap rate for an area, and many of the properties do not post accurate net operating incomes - what is the best way to estimate? I heard dividing the gross income/rental income by half is best way to estimate net operating income? Multiple questions here I know, thanks for your help!!! (I'm specifically interested in proving the cap rate in Lincoln Park for a 4-unit building).