~snip~
If you know Bitmain you would realize this is nothing new. If I recall they have been doing this since the Antminer S5 days.
It's actually a good thing that if you order a miner from them and it comes with dust, it means it was tested at least.
Because they sometimes assemble their miners, don't test and ship them half way across the world and when they are plugged in they are dead on arrive. Then they require a trip back half way across the world.
That was a wise answer, a bit agree with that.
The most suspected (by most people) thing is that Bitmain sold Miner that been used (as we know as silent mining that does by Bitmain), that article showed some images that new received mining equipment with a lot of dust on its heatsink. I'm not sure about which the right one.
But for me, that was easy.
If you trust them, buy it!
If you doubt, don't even to see their products. Leave it!