There are a lot of Mishnayos and Gemoros discussing שומת דיינים. E.g. Kesubos 99b:
"מתני׳: שום הדיינין שפיחתו שתות או הוסיפו שתות מכרן בטל"
"The assessment of the judges of the value of a piece of property in order to sell it is as follows: Where they decreased the price by one-sixth of its market value or added one-sixth to its market value, their sale is void."
I've read a lot of Meforshim inc. Rambam (Hilchot Mechira) and could not find a clear description of the process of assessment, especially how it can lead to gross errors.
I'm looking for a Halachic summary of how it is done, what people are involved, what estimates are taken into account, who sets the nominal or market value etc.