。
People who break their promises aren't trusted.
Literal
Promise [obj-を] break person [topic-は] not-be-trusted-[passive-される].
A maxim-style statement with a relative clause modifying 人. The predicate 信用される is the passive of 信用する ('to trust'), and the negative gives 'is not trusted.' Generic 人 and generic は make this read as a general truth rather than about any specific person.