You undergo an apprenticeship with a respected Curandero who has the experience and knowledge.

I'm not exactly sure about the in's and out's, but it involves learning about the jungle plants, doing plant 'dietas' in isolation, Ayahuasca ceremonies, learning icaros, and how to see illness, control the mareacion, how to cure, etc, etc. It roughly takes 2 years minimum to learn the bare basics.

They are different from someone who drinks Ayahuasca, because they have knowledge and ability that a drinker does not have, from the training and plant knowledge assimilated. They can actively work in the realms and manipulate it. A drinker does not have the same ability, and is merely passive.

I seriously doubt that.

I think you mean that 'some' retreat OWNERS might do. They are the ones who are the businessmen running the show, not the Curandero's.