From the perspective of law, it matters very much how that defect rate is reached, because intent matters more than the outcome itself.

If you have a 10% defect rate for unavoidable causes, that sucks. If you have a 10% defect rate because you chose to cut all corners and cheap out on every aspect of your manufacturing and testing, that sucks but it's legal. However, if you have a 5% defect rate and intentionally choose to mix in extra 5% of known defective units - that's fraud.

Depends on the industry. There are industries where high defect rates are an accepted norm. These are not necessarily codified. For example: if you order fresh fruit/vegetables in bulk, a certain percentage always arrive below acceptable quality. That is simply a norm in the industry. You are free to inspect/reject as much as you want, but nobody will want to sell to you if you make a lawsuit out of every bad apple.

I don't think what you described differs from the GP. The bad apples were not thrown into the lot intentionally.