1) its way harder than you'd expect as many compounds are safe in low concentrations and have other uses. Take TATP- triacetone-triperoxide. yes, the peroxide and acetone(nailpolish remover) in most people's bathrooms should never be mixed.

2) might want to look up how often firearms make it onboard in carry on bagage accidentally. This isn't the typical snarky use of that phrase- it's just so insanely common people don't want to beleive it.