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Data pre-processing is an important part of the data mining process, because quality of the data used for an analysis mirrors in the results. If we have high-quality input data, then we will have high-quality results. The representation and quality of the instance data is very important, as analysing data not carefully screened for problems can produce misleading results. Thus, the representation and quality of data is first and foremost before running an analysis. Data pre-processing includes cleaning, normalization, transformation, feature extraction and selection, etc. The article is focused on work with real data obtained from automotive industry related to breakdowns from the car body work. The presented analysis is provided as a partial result of the research and will serve to further investigation in the problem area.