The value of a property is what an able buyer and willing seller agree to.
The appraisal order by the lender is to assure they can resell the mortgage.
Confusing the two will cause the wrong conclusion.
There are eight go/no go, parameters for a home mortgage. Most of these are not even looked at until the last week of the process. Then 5 days before closing the lender backs out, after the buyer has paid for a inspection and the appraisal.
Sellers need to confirm buyers have sufficient cash on hand to overcome the banks Dobbs/Franks Consumer Protection Act requirements.
Buyers need to receive a 'Clear-to-Close' before making a purchase offer. The means the buyer has passed underwriting requirements and there won't be any "found something in past tax returns' that will be cited as the reason for the bank to pull out of their agreement.
Allowing a third party, who has different objectives, to establish the 'value' of a home seldom ends well.
There are two big bank lenders who are notorious for leaving buyers at the alter. Sellers must have the courage to kick any offer from a buyer who is packing paper from these banks to the curb immediately.