You may not like it, but the UAD and the UCDP were a direct result of many in the secondary market not trusting appraisers
The C and Q ratings are an effort at standardization, a standardization that is vague at best. And using G / A / P vs C2, C3, C4 is a variation but one that, though defined, isn't very descriptive. How can we argue that our values are within 5% or even 10% when the quality rates by their very definition, are closer to 20% per rating? Why not use P, F, A, G, X in lieu of C1 - C5? Can the computer not read the one and can the other? Neither system prevents an appraiser from "lying".
But why would Fannie, et al, not focus upon the central issue of comp selection? In an urban area, how could you NOT find 3 comps for a typical home? Why would you EVER need to make a quality or condition adjustment? If you have confined your search area to be so restricted that you have eliminated everything but the three closest sales, then certainly one is likely to be an outlier.
Eliminate the appraisal entirely if you cannot trust your appraiser to be truthful enough to use the best sales and not be told that you have to vet every sale within a mile, or three miles, whatever - etc etc. And frankly, Fannie Mae, FHA etc are to blame for the situation by attempting to shoehorn restrictions upon appraisers that result in a Pavlovian response of attempting to tell you (Fannie) what they think you want to hear. Their manuals are not guidelines in a modern mobile society, they are guidelines designed for the 1950s and redlining. They create imaginary boundaries out of whole cloth then wonders why appraisers are confused.
I can't think of 1 in 10 people who bought a house in a particular "neighborhood". They looked at numerous neighborhoods. In parts of the south they cannot even base their choice on school districts due to forced bussing. When two working parties, most families seek the optimum distance between where each work and where their kids go to school. And often have to sacrifice one or the other. One of my nephews has a child subject to life-threatening seizures and they chose a home near a medical unit, secondary importance to their teaching jobs, as he teaches in one school and she in a totally different town 10 miles away. Another family member lives within 3 miles of her hospital because she has to be within 10 minutes of the hospital when on call. Another works 25 miles away from his wife's place of work and thus they live in yet a third town. The idea that "By Gawd, we'll live here or else we won't buy..." is nuts, and if nuts, then why is it an issue, and why does the choice of comps become influenced by proximity which limits the appraiser to a few "fannie selected" comps from a given distance from the subject - an artificial paradigm created entirely out of whole cloth by Fannie (and FHA).
So in many places the very notion of "neighborhood" is ridiculous on the face of it, but as an arcane artifact of the past, appraisers are sometimes conflicted by satisfying Fannie and FHA while being put in the box of using an inappropriate comp due to the lack of sales in a too confined neighborhood, or facing a slew of computer generated "stips" for failing to match the "fannie box".