that was one of the things that surprised me on an early saturday bike ride, also in regards to street crime in japan, at least in my experience it is so exceedingly rare that most people there are incredibly naive to it.
One example are the notoriously expensive bars in Roppongi, at night there will be touts in the streets trying to convince tourists to join them for a night of drinking. They'll then go to the bar that hired those touts where, after a night of drinking, the tourists will be presented with a bill that's the equivalent of getting robbed.
Long and short, don't let someone on the street talk you into going into a bar or tea shop or whatever, and especially don't follow them to a second location.
The line for "acceptable robbery" was "no physical violence" + "someone consensually gives me their money."
Which is still possible (and easily doable if that mark is drunk), but is substantially different from American (and European?) style physical robbery.