15. A computer-readable, non-transitory storage medium having a computer program stored thereon for causing a suitably programmed computer system to process by one or more processors computer-program code by performing a method for generating recommendations of alternative unique items when the computer program is executed on the suitably programmed computer system, the method comprising: receiving electronic data indicating a selection of a selected item; calculating, using a computer system, a customization score for each of a plurality of alternative unique items, the customization score representing an estimated preference impact of a difference between at least one customization attribute of the selected item and at least one customization attribute of the alternative unique item; calculating, using the computer system, a condition score for each of the plurality of alternative unique items, the condition score representing an estimated preference impact of a difference between at least one condition attribute of the selected item and at least one condition attribute of the alternative unique item; generating, using the computer system, a dissimilarity penalty for each of the plurality of alternative unique items by combining at least the customization score and the condition score; and generating, using the computer system, a recommendation of alternative unique items, the recommendation comprising a ranking of at least a portion of the plurality of alternative unique items, the ranking based at least partially on the generated dissimilarity penalties; wherein the computer system comprises a computer processor and electronic memory.
15. A computer-readable, non-transitory storage medium having a computer program stored thereon for causing a suitably programmed computer system to process by one or more processors computer-program code by performing a method for generating recommendations of alternative unique items when the computer program is executed on the suitably programmed computer system, the method comprising: receiving electronic data indicating a selection of a selected item; calculating, using a computer system, a customization score for each of a plurality of alternative unique items, the customization score representing an estimated preference impact of a difference between at least one customization attribute of the selected item and at least one customization attribute of the alternative unique item; calculating, using the computer system, a condition score for each of the plurality of alternative unique items, the condition score representing an estimated preference impact of a difference between at least one condition attribute of the selected item and at least one condition attribute of the alternative unique item; generating, using the computer system, a dissimilarity penalty for each of the plurality of alternative unique items by combining at least the customization score and the condition score; and generating, using the computer system, a recommendation of alternative unique items, the recommendation comprising a ranking of at least a portion of the plurality of alternative unique items, the ranking based at least partially on the generated dissimilarity penalties; wherein the computer system comprises a computer processor and electronic memory. 18. The computer-readable, non-transitory storage medium of claim 15 , wherein the estimated preference impact of the difference between at least one condition attribute of the selected item and at least one condition attribute of the alternative unique item comprises an estimated price impact.