I've seen this occasionally, also sometimes Treasury Agents. But not checking everybody, only targeting specific people. I think they do this if they have been tipped off that someone on a specific flight is carrying some kind of contraband out--or in Treasury's case, a wad of undeclared cash > $10K. Once on my way to Asia and traveling alone, I was once pulled aside on the jetway by Treasury and given a brief questioning. No it wasn't me with the spare $10K that day! At the time, wasn't sure whether to be flattered that they thought I looked wealthy or insulted that I looked shifty.