As in many other areas, the notion of comparison is important in real estate appraisal. It is most convenient and practical to estimate the market value of a subject property based on the comparison of its characteristics with those of similar properties (comparables). Convergence to the similarity is the approach that systematically excludes the difference because, besides being convenient, results emerge more easily. Yet what actually exist in practice are properties often different from the subject. Is it possible to use rather uncomparable properties, in inverse direction, to estimate the market value of the subject property? It is the issue of interest in this paper which aims to enlighten the process of comparison by proceeding with uncomparable properties. Based on the use of a large dataset from Montreal (Canada), some coherent empirical results are presented.