He is a dubious character.

他是一个靠不住的人。

youdao

Considering Williams has such a dubious character, perhaps he twisted the truth in other instances.

FORBES: Book Review

Take this outdoors without having wiped it down with a lint-free cloth, and people will start to make dubious assumptions about your character.

ENGADGET: Gigabyte X11 review: slim and powerful but not without flaws