Have you ever bought any fake commodities?What's the result?

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I recently bought an MP4 from a small shop.But originally I asked for an MP5,and the assistant showed me one. When packing,I didn't noticed and the assistant turned her back to me.After returned home,I found the big mistake.The MP5 turned into MP4.But when I went to the same shop the following day,the assistant said I can change it but only on the same day I bought that.I 've got no chance to change that anymore. This experience really annoyed me a lot. Have got such experiences?