We were notified quite quickly when we got a speeding ticket coming of an Autobahn in Stuttgart. Sixt didn't pay the fine but charged us an admin fee to tell us that we have incurred a speeding ticket. A couple of weeks later we then received a letter from Stuttgart council with details in German of how to pay.
I was able to pay the fine through my local bank in the UK but they charged a handling fee of about £10 on top of the fine and Sixts' admin fee.
Hertz on the other hand have paid the fine and passed on the cost plus an admin fee to the customer in the past and saved a lot of hassle therefore giving me a reason not to use Sixt in future!