@book { ComplaintManagementandInternalMarketing,
    title = "Complaint Management and Internal Marketing",
    author = "Malte {Kempen}",
    year = "2009",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836624404",
    url = "https://m.diplom.de/document/226447"
}