Everyone seems to forget there is usually 3 parties invested in a real estate transaction.
The idea that two parties can agree on a price, whether it is supported or not, then ask a third party to take on almost all of the risk by financing the deal whether or not it makes sense financially for the third party is completely naive.
This is why market value is not just a price two parties agree to. There is a third party!
You want to eliminate the third party, then no need for an appraiser.