I am sure the cells are good during pack assembly, but they dont keep them sitting on a shelf for months to weed out stinkers so by the time the packs are built, packed, shipped, distributed, and finally get in your hands, bad cells have self-discharged and puffed.
My first go at HK packs , 6S 20C packs, was pretty bad... had to do lots of repairs... but the next year i got a few dozen more and all arrived and are still working perfectly.
last year i got a dozen nano-tech packs for my KMX and again, all in perfect condition..
I ordered a few 8ah 5S packs last week or so.. waiting for them to arrive.. fingers crossed..
The guys working in the warehouse packing boxes likely ( i cannot say for sure.. duh .. nobody can ) do not check each pack by opening each box, unwrapping the bubble wrap and checking cells .... not happening at the prices we pay.. fact of life...
no company would intentionally ship bad product, that's just nuts, but the higher the quality control, the higher the pricetag.. if you want perfect packs you can go ahead and pay 200$ for a premium brand lipo pack rated at 100C... but for that price you can get 4x the capacity at ebike C rates..