@book { MarketingfrfreieGesundheitsberater,
    title = "Marketing für freie Gesundheitsberater",
    author = "Cornelia {Fey}",
    year = "2015",
    publisher = "via tolino media",
    address = "München, Deutschland",
    url = "https://tolino.openpublishing.com/document/1372188"
}