I've often wondered, standing in those long lines at airports, how
exactly those officials decide who is "suspicious looking", & who isn't. I have never once been stopped (mind you, I am of incredibly wholesome appearance!
) ... but I formed the impression that some people were stopped over & over again, because of some preconceived notion on the part of customs officials about the likely appearance of "type of person" who might be a drug carrier, especially.
I vividly recall, on train trip from A to B across European borders some years ago, all of us being woken at the crack of dawn for a routine customs check. The one couple who was singled out for a super-thorough check was predictable: young, not "well off" travelers exactly & "untidy looking". Poor things, they had to pull out every single thing from their back-backs, open every single jar of vitamins, etc & explain what each item was.... I'm certain it'd happened to them time & time again. Purely because of their appearance .