信不过 is a fixed verb-complement phrase meaning 'cannot trust' or 'mistrust'. It is formed by the verb 信 (to trust) plus the complement 不过 (cannot pass), indicating that trust cannot be achieved. It can be used as a predicate (信不过他 'cannot trust him') or as an attributive modifier (信不过的人 'an untrustworthy person'). The antonym is 信得过 (trustworthy). Note: the full pronunciation is xìn bu guò, though the pinyin field here is abbreviated.