Originally Posted by AngryMiller

Hmmm, you go into a store. The guy in front of you does blasting for a living. He touches the door handle, leaving a few parts per million on the handle. You come along behind him and touch the same handle. You've just picked up some RDX even though you've never done any blasting at all.

This was in the UK and the point I was trying to make was why bother swabbing someone's hand? If he touched something then there would be traces on the luggage handles.