。
I don't trust what that guy says.
Literal
I [topic-は] that-guy [possessive-の] saying [thing-こと] [topic-は] trust-do-not-[explanation-んだ].
奴 ('guy, fellow') is casual and slightly rough. 奴の言うこと ('the thing that guy says') is a relative-clause-plus-nominalizer construction. Topic-marking は on the inner clause gives it contrastive emphasis. 信用しない is the plain negative.