This is a key point. I'm sure Facebook carries a trade credit insurance policy and those policies require collections and court if a person/entity doesn't pay. So in other words they certainly ate the bill if they didn't make him pay.

The only logical reason to do this is fear of the truth coming out in court and the ensuing press coverage to damage their stock value.

Anyone have an idea about FB's liability if they were subpoenaed for fraud and the investigators found internal emails discussing the fake click problem and their decision to ignore it. Seems criminal to me.

This... It at least seems to show a lack of faith in your product if you sometimes don't worry about collecting payment.

I think it tells you everything you need to know about how much faith Facebook have in their own product.

Assuming that they did write off the bill it is curious that they didn't try and keep the client. Why not just fix the problem and rerun the campaign for free?