A cheap way to likely destroy circuit boards is to spray boards with common household bleach. A wetting mist would probably do, don't have to soak everything down. Unless boards are protected by a milspec mask, the chlorine (and salts) will corrode connections and pathways for the electrons.
Full disclosure…. I've not personally observed the effect of bleach. I have observed the effect of dilute chlorine gas during an industrial gas release. Milspec boards keep on ticking. Commercial boards fail in a few days.
Why should they do it when they can simply keep working for the Chinese and save themselves troubles?