I'm almost convinced at this point that clones are being sabotaged intentionally. My buddy just got some "reputable" clones from a company in Michigan and they exploded with white powdery mildew a few weeks after being in his room.
Seed only...
I haven't had powdery mildew or bugs other than fungus gnats in over a year.
Sealed room (no exhausts or intakes from outdoors)
Clean shoes (Wear shoes/slippers specifically for grow so your not tracking stuff in)
Don't let people in you grow that grow. (I know it sucks but share pics its not worth the risk)
I'm probably going to sound crazy but when I leave the grow store before I get in my car I literally spray my shoes with lysol just in case.