I know crims come in all shapes and sizes, and from all backgrounds...but I'd say you can quite often, by look, tell who's 'been in a bit of bother' in the past.
A sociology student who I worked with for a while told me it wasn't ethical to say it. Not sure I'd agree...if you're walking down the street and you see someone who looks like a nasty piece of work, you'd avoid them, right?
Not sure what's so wrong with what I said...???