9. A computer-implemented method for generating recommendations of alternative unique items, the computer-implemented 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.
9. A computer-implemented method for generating recommendations of alternative unique items, the computer-implemented 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. 10. The computer-implemented method of claim 9 , wherein the at least one condition attribute of the selected and alternative unique items describes at least one of the following: a number of miles an automobile has been driven, whether an automobile's title is clean, whether an automobile has been in an accident.