Mafia competition harms customers through violence against rival clients [causal]
Among the consequences of mafia protection, those associated with violent competition among mafiosi are possibly the worst for customers. Kidnaping, extortion, and damage to property at the expense of a rival's client are common ways of undermining his credibility in anticipation of a more direct attack.
Diego Gambetta, The Sicilian Mafia The Busi…, loc. 500