It's not a matter of paying more for a non REO lot.
The appraiser has to explore both sides of the issue. Arriving at MV means researching and analyizing why buyers are paying more, as well as less, for similar properties.
A certain amount of research shows you that buyers are paying less for REO lots. Fine. But why do you stop there? Unless you dof urther research, it is unknown if the only reason buyers are paying more for private sale lots is the REO status of some lots/ You have to see if the owner lots are offering private financing, cash back at closing, or other terms. If any of that accounts for higher prices, it has to be disclosed and possibly adjusted for. If research shows none of that is present, then you can state the price difference is just REO status.
It's about a reason for not paying market value for the REO.
Here is the fallacy about your thinking of MV. Once again, you are starting a report with the assumption that the higher sales are MV prices. You did a chart with possibly dis similar land sales lumped together, and assume a 20% higher price for non REO's.. But you havent' done the report yet, you don't even know what MV is? Should MV be on the high side for subject lot? Is the area troubled, why are there so many REO's present? Is owner financing or terms making private sales sell for more? How do you know, if you don't even ask the questions? It may turn out that the 20% higher sales are MV, but you can't start a report assuming that, and then doing no other research that would disprove your own assumption.
Whether you want to believe it or not, many issues come up with these properties. Title, legality of foreclosure, multiple banks...just talked to one where another owner was found. People buying lots are investing in building. I have one lot that the buyer bought the land for $750k. He turned around and has it listed for $1,200,000. (He won't get that, but he'll probably get around $900-950k)
Another lot that has a house was purchased for $950 as a REO. MV is about $1,550,000.
These distressed sales are affecting the market, but they are running fairly parallel.