I will have to disagree about "leísmo" and "loísmo" here: When you say "don't believe her/him", we say "no le creas" (
Indirect Object), because in Spanish we believe things, not people themselves and we are rather talking about the thing they say, which we assume is false.
But we say "no lo/la creas" (
Direct Object) when it's the thing itself that mustn't be believed.
So when talking about a person, it's "loísmo", rather than "leísmo" what sounds strange.
-
Juan te está mintiendo; no
le creas.
-
Ana es una mentirosa; no
le creas.
-
Los niños dicen que tú les diste dulces; no
les creo.
-
Tus amigas están equivocadas; no
les creas.
-
Esta noticia es falsa; no
la creas.
-
Lo que te dijeron es mentira; no
lo creas.
- Qué
historias más
ridículas me has contado; no
las creo. (Or "no
te creo", if you mean to say "I don't believe what you're saying").
- Qué
comentarios tan
absurdos; no
los creo.