Fall for (someone or something) hook, line and sinker verb phrase
To have strong feelings of love for someone or a strong interest in something that makes you unable to think in a sensible way
When I first saw that car, I fell for it hook, line, and sinker.
He falls for Lisa hook, line, and sinker.
To have an unquestioning belief in something untrue that someone tells you
I told them that I had lost my purse, and they fell for it hook, line, and sinker and gave me money.
The verb "fall" should be conjugated according to its tense.
To decide to believe someone‘s saying although they may not tell the truth
He said that he was late because he had an accident and I gave him the benefit of the doubt.