The problem is that a genuine certified aircraft part has a huge cost adder attached. Between certification and testing and liability insurance, a $1 part can cost 50-60 bucks. So the incentive to cheat is quite strong.
I worked at a company that builds piston engines for general aviation. We had fasteners in stores that we sold for over $100 apiece as “Genuine OEM Parts”.
And here I thought government parts were ridiculously expensive. How wrong I was!