Usages of ser de fiar
Tu compañero de piso no es de fiar.
Your flatmate isn't trustworthy.
Mi hermano es de fiar: nunca cuenta un secreto.
My brother is trustworthy: he never tells a secret.
Ese tipo no es de fiar, y encima hace trampas.
That guy isn't trustworthy, and on top of that he cheats.
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