Why do “reputable” websites allow blatant financial fraud?

I hope I can post this here. Brief background: Recently my father came to me and said he had found a great offer for fixed-term deposits online and had registered somewhere with his email and telephone number. An employee promptly contacted him and sent him an alleged fixed-term deposit offer from Santander by email. I then took a closer look at it and with a little research I came across a warning from BaFin about this intermediary. Of course I have you