I've never made a customer pay for my mistakes. But I sure as hell have made them pay for theirs (especially where said customers have been warned well in advance).
The best time was when I was in a meeting explaining that a system was unstable and needed to be migrated from ASAP. Said system had been running for a long time, was unsupported, and had been flagged as an issue for a very long time. Management scoffed and said it was fine. In the middle of the meeting phones started ringing. Guess which system had just fallen in a heap and was now causing a massive outage!