@David Greyshock
I started off in finance. My job was to recognize mispricings in the market place. Everyone had their own valuation models and they used them to calculate their own internal fair value. If the market was under priced relative to this you bought if it was overvalued you sold. There are dozens of pricing models for stocks no one model is right.
When you look at appraisals, what is the purpose of the appraisal? I would argue the primary focus off an appraisal is to protect the lenders interests and a bi product of that is protecting the buyer's interest. The bank doesn't look at single family and small multifamily homes from the buyer's(investor) point of view. They look at it is what is the current market price in the area and am I paying over market value. Which is fine, since they are putting down 80% of the money.
Now when you start to look at commercial properties valuations tend to get cloudier because the lenders will look at it as an investment. They will look at the cash flows of the properties and they will make adjustments to their inputs relative to a variety of factors regarding the property. One example would be quality of cashflow. If you have a retail strip full of national chains vs nail salons. The valuation would be different depending on who your tenants are, with all other things the same.
With that all being said, currently single family homes and small multifamily are only viewed as owner occupant and their values are derived by comparable sales. There are plenty of turnkey operators that sale at or below market value so as a buyer there is no reason to stretch to make something work.
Lastly, one thing that is not addressed in the appraisal. It is the quality of the property manager. I would argue the quality of the property manager is more important to the value of the property from the investors point of view than what the house next door sold for. A bad property manager will destroy your investment, just like management of a company you own stock in. They can either create value for you or destroy it. This will never be adjusted for in an appraisal.