Republics sustain public trust better because public instruction is more severe

Evidence

As long as fede pubblica always dominated fede privata the polity itself might take the form of either a monarchy or a republic. Genovesi, like Rousseau, however, believed that true republics were more likely to succeed, for in a republic public instruction is ‘more severe’; there is less luxury - there are fewer purely private goods - and as a result it is more ‘creditable’ (‘si puo avere piu credito in una repubblica che in una monarchia’) and ‘trust [fede pubblica] is more rigorously upheld’ (1803: 57-8). — Diego Gambetta, Trust - Making and Breaking Cooperative…, 1750