Can the intermediary be held liable for recourse due to inadequate submission?

In my experience, it is about weighing the anger you feel because mistakes were made against the anger you get if you go to court. I have been through a few lawsuits and my advice is: if possible, avoid it. But of course, that does not mean never pursuing a lawsuit. Fuchsbau says: "lasst euch von einem Fachanwalt beraten!" That would be an important first step if you decide to go for it ... and that already costs someone something. The annoying thing is: You can also lose. One - not quite easy - method is: to not care. If you can manage that, life often becomes easier and I find that - if genuine - quite an honorable attitude :)