to trust, rely on, to give credit, let someone buy on credit
Te dije que no te podías fiar de él.
I told you you couldn't trust him.
Por cierto, me tendrás que fiar.
By the way, you'll have to trust me.
— Por un puñado de dólares (1964)
You can't trust anyone.
No me puedo fiar de mi libro de texto.
I can't rely on my textbook.