be completely taken in 信以为真

“信以为真”，汉语成语，意思是以为某件事是真的，指把假的当作真的。可以翻译为“accept something(usu false) to be true，be completely taken in”。

例句：

他这人很容易轻信，别人说什么他都信以为真。

He is so credulous that he believes whatever is said.

别对那些道听途说都信以为真。

Don't believe all the gossip you hear.