The 'do not talk to strangers' skill, streetwise teaches individuals the best way to walk through The Boroughs and not get mugged. It's also just a reflection of survival inside the large city environment of Arx, and the equivalent of the 'survival' skill for urban areas. It'll stop someone from being hit by a cart.
0: Throwing tons of silver around in the Lower Boroughs in front of thugs might feel unwise.
1: You know a guy who knows a guy.
2: You are aware that the black market is not, in fact, a market painted black, and can find fences (who are not wood).
3: Familiar enough with the different underworld figures that you can track people down without excessive numbers of stabbings.
4: You know the complicated ebb and flow of status in the Lower Boroughs, and how to manipulate it.
5: Anyone that crosses you should stay clear of seedy parts of Arvum.
6: Most Arvani don't know other continents exist. You already have a global criminal enterprise.