If it gets to court, terms about not having third party audits are unlikely to be worth the paper they're not printed on to Facebook. The customer's lawyers are presumably going to use whatever discovery process applies before the case is heard to open up every can of worms they can find, and Facebook are presumably going to have no choice but to comply with requests for information even if they'd prefer to keep it to themselves.

If the customer's lawyers discover evidence of systematic failures (intentional or otherwise) and get that information into the public record, the resulting damage to Facebook could be astronomical. The risk doesn't necessarily come only from the original case. It could lead to things like class action suits, or even investigation for criminal fraud that could have FB executives personally facing jail time, depending on which legal system(s) applied. Conceivably, that could pose an existential threat to Facebook itself, though I'd be very surprised if anything that serious was going wrong and they hadn't discovered and dealt with it themselves.

Assuming the above is approximately correct in whatever jurisdiction applied to the original dispute/law suit, I imagine you'd have to be talking orders of magnitude more money before it was worth it for FB to fight a well funded, determined opponent who has real evidence on their side in court. With their war chest, I'd expect settling out of court if necessary and then dropping the matter as quickly and quietly as possible to be their preferred option under almost any realistic conditions.

In trying to find Google's policy and handling, I came across this interesting (2006) analysis[1]. Apparently they do pursue this on a case by case basis.

[1] http://static.googleusercontent.com/media/www.google.com/en/...

This makes sense. I go to Facebook to catch up on friends. Google is more when I'm actually searching for something. I would think that Google could charge a higher premium as a result.