Part of the appraiser's job is to exclude sales, not just include sales. The excluded sales are those with atypical terms or motivations, to the point where it affected price either far below or far above what we refer to as "market value" ..and market value only happens at the terms defined in the market value definition used in the appraisal. The MV def describes what the TYPICALLY motivated buyer would pay, for a property reasonably exposed to open market. This property was not listed or offered to anyone else thus had no exposure to the open market Buyer had atypical motivations who vastly overpaid, result is the buyer did not act prudently. Acting prudently is in the MV definition, but it's not sexy so appraisers tend to overlook it. Even if this buyer was smart or well informed/ well advised, they chose to overpay for personal reasons, thus did not act prudently.
Though an appraiser can adjust for non MV terms or motivations, when the adjustment itself becomes outlandish that is the break point to exclude the sale.
You can comment on the sale in narrative and explain why you did not include it on the grid.
DEFINITION OF MARKET VALUE: The most probable price which a property should bring in a competitive and open market under all conditions requisite to a fair sale, the buyer and seller, each acting prudently, knowledgeably and assuming the price is not affected by undue stimulus. Implicit in this definition is the consummation of a sale as of a specified date and the passing of title from seller to buyer under conditions whereby: (1) buyer and seller are typically motivated; (2) both parties are well informed or well advised, and each acting in what he or she considers his or her own best interest; (3) a reasonable time is allowed for exposure in the open market; (4) payment is made in terms of cash in U. S. dollars or in terms of financial arrangements comparable thereto; and (5) the price represents the normal consideration for the property sold unaffected by special or creative financing or sales concessions* granted by anyone associated with the sale.