@book { NeueKundengewinnenvorhandeneKundenbinden,
    title = "Neue Kunden gewinnen - vorhandene Kunden binden",
    author = "M.-Fatih {Karasu}",
    year = "2009",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836636247",
    url = "https://m.diplom.de/document/227223"
}