So, your main point is that you don't have any idea what "most probable" means? Did your mentor ever tell you that one sale doesn't make a market? If one sale doesn't make a market, how could one sale possibly reflect "the" likely impact of a single feature on prices? Those appraisers who steadfastly refuse to learn, or even just understand, "anything" about data analysis or statistics, even though myriad sources outside of appraisal have been developing the field for years, are why requests for these data are being developed. As a whole, appraisers learn what questions will be asked when their reports are delivered. Then, they deliver reports with the sole intent of insuring the fewest number of those questions will be asked by dumping garbage in their reports. Take any issue, and it happens. And dumping one sale in a report and saying, "see, covered it" is just another way of dumping the garbage. Actual analysis, on the other hand, can actually support the conclusion reached by the appraiser.
The following is an excerpt from the last residential report I delivered. Every aspect of the subject was "bracketed" by the 5 sales discussed. A focus on "bracketing" removes focus from "analyzing."
"the prices of these sales all fall within a narrow range (the 5 most heavily weighted had a coefficient of variation (COV) of about 5%), but their property characteristics varied widely. The following are characteristics commonly found to influence sale prices of residential properties, with the COV of that characteristic (in parentheses) for these 5 sales: Age (44%); GLA (30%); Finished basement (75%); Unfinished basement (32%); Baths (24%); Garage stalls (87%)."