Another way to distinguish when an object is direct or indirect is to analyze the nature of the verb as it functions inside the sentence. This way we will be able to recognize verbs like saludar, ayudar, respetar, visitar, ver, estimar, apreciar, odiar + a + a person or group of people. In all these cases there is the preposition A before the object but it is what we call “ la A personal” and the objects are direct. Therefore we would say: LO ODIO, LAS RESPETO, LOS AYUDO, etc.
INDIRECT OBJECT PRONOUNS:
There is nothing between the verbs above and the person. We cannot say “yo respeto algo a alguien”.
However, we say DAR ALGO A ALGUIEN, PEDIR ALGO A ALGUIEN, DECIR ALGO A ALGUIEN, TRAER ALGO A ALGUIEN, CONTAR ALGO A ALGUIEN. Even if the ALGO is not mentioned, it is implicit. Therefore the ALGUIEN is an INDIRECT OBJECT and requires an Indirect Object Pronoun to replace it.
For example:
Ayer ví a Rosa y LE di el informe
Cuando visito a mis sobrinos siempre LES llevo regalos.
Pedí dinero a mi amigo. LE pedí cien dólares.