I am no newbie far from that.It has more to do with that you should never exceed your MAXIMUM recommended total Debt:The formula for that was in Finland Landlords newest magazine form spring 2021.Maximum DEBT FORMULA is and this is what they recommend in Finland.Your work GROSS income/month X (means multiply by) 12.5+ x (MULTIPLY BY) 4.5+LANDLORD (+stocks) GROSS income /YEAR (Note not /month) x (MULTIPLY BY) 4.5Please note in FINLAND we do not have normally SUPER USA Salaries.

Then take the SF and multiply by $300 - $400.

All you can hope for is that you can point out a factual error - however, unless it is square footage, and even that can be tricky if they measured the house themselves, it is unlikely to change the value much at all, as the appraisal is essentially price per square foot (based on comps) multiplied by square footage.

Also, if you are marketing to buy and hold investors you can use Gross rent multiplier to determine your asking price.

Meaning, you would determine that after repair value (based on the comparables to the house you are looking at) and multiply that value by 65% or 70% (based on how much of a margin you want) and then subtract your rehab costs.

Gross Rental Income:$142,800Gross Rental Multiplier:9.8Total Annual Exps:$35,000Annual Net Operating Income:$102,560Janitor Expense ($/src):$0/Water Expense ($/src):$801/ActualRepairs/Decor Expense ($/src):$0/ Total Monthly Income:$11,463Tax Amount:$38,000Expense Source:CombinationNet Oper Income Year:2016Fuel Expense ($/src):$0/ActualScavenger Expense ($/src):$0/Other Expense ($/src):$0/ Total Annual Income:$137,560Tax Year:2015Expense Year:2016Cap Rate:7.3Electricity Expense ($/src):$4,315/ActualInsurance Expense ($/src):$0/Apartment Info# UnitsRoomsBedroomsBaths (F/H)Monthly Income Range (Min-Max)Type 1102011700-790Type 241222900-1000Type 30000Type 40000Type 50000Type 60000Type 70000

Mathematically, it is simply the inverse of the Gross Rent Multiplier (GRM), using monthly rather than annual rents.

So  in doing due diligence I'm apply the GRM, but the subject property rents vary how would I calculate GRM effectively?

This then allows him to add those transparent numbers up to a total estimated hours, ( giving him the practice and confidence in his estimating ability)that can then be multiplied by the $30/hr add  in 10% For unforeseen issues and you then have a transparent number that you can both start to work from. 

To crunch a few numbers, 6 hours/day at $20/hr multiplied by 6 days equals $720 in saved costs.