@book { Kundenakquise,
    title = "Kundenakquise",
    author = "Stephan {Preuß}",
    year = "2005",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832490560",
    url = "https://m.diplom.de/document/224215"
}