Black market business in Renaissance Italy was booming. Muggings in the major cities were fairly common, as were murders. Often, strollers were attacked in the dead of night, killed, robbed and then rolled into the nearest river or canal. Even if a thief merely stole, rather than killed, the penalties if caught were often unduly harsh. Torture was common. Thieves were put in stocks and sometimes even publically executed.
In order to avoid punishment, thieves often created bonds of trust amongst each other. Each was supposed to tell the rest his dirty secrets, which meant that each thief potentially held his comrades' lives in his hands.