Yep, they are serious business, not one of the dodgy ones that send out as many threatening letters as possible and hope that a few pay. They'll actually go to court, or did so in the past, with a huge army of lawyers. When the "fliegende gerichtsstand" was abolished they got more selective with which cases they actually took to court, depending on the city they'd have to go to. Before, all cases were handled in Munich, and the judges there were pretty much rubber-stamping the cases in favor of WF.