In reading one of your lessons on Prepositions, I saw "fiarse de" i.e: fiarse de algo, Roberto, etc.
I was surprised that "de" is used here and not "a" for a person, or "en".
1) Could you help me understand why "de" is used here?
2) Can these forms be used and if so, what would they mean? and if not, why not?
fiarse en algo
fiarse a algo