Which, of course, makes it perfectly acceptable?

No, but if Microsoft asked for wav files, and a contractor delivered them, is Microsoft at fault if the contractor used a pirated editing software?

Liable? I hope so. And then they can pass the buck on.

Why would Microsoft be liable?

Do you check if your butcher has illegally bought his knife? Should you be liable, if so?

Hmm... you may be right. But on the other hand, is the steak licensed and copyrighted?

It's not, but metaphors and analogies only go so far :)

That sort of shit is relevant only to lawyers. A salaried sound designer could have lied to Microsoft just as easily. The nature of the offense isn't actually being changed in any practical sense between the two scenarios.