There's also the issue that, if you accept one (1) part from your supplier that doesn't meet some specification in the contract, you have just unilaterally renegotiated that specification for the rest of the contract. After you have done this, your supplier can sue you if you later reject a part that fails the contract spec but exceeds the spec of the worst part you have ever accepted.

What this means is that, for outsourced parts, quality costs twice. The first time, because your supplier will charge you more for the tight specs. The second time, because you have to do your own QA when you receive the parts, and the way that contract enforcement works means that your QA has to be at least as rigorous as the vendor's, and ideally more so, lest your vendor know more about your parts than you do.

--Shannon