It sounds like some of those shamans are starting to show their true colours. I was told by someone who's visited various countries in South America since the 70's that Ayahuasca never used to be seen as a healing tonic in the way it's used now, it was used mainly by shamans to "see" things that weren't able to be seen in a normal state. The healing aspect seems to have been packaged into the experience mostly for the tourist dollar.

Tribal battles were common and the shamans from each village would wage war against each other on the spiritual plane as well as the earthly plane. They would use Ayahuasca to send poison darts to other shamans and enemies and unscrupulous shamans would use it to attack anyone they didn't like, some of them just hate gringos.

That's why intentions are so powerful & you tend to get what you expect or need from Ayahuasca if you prepare for it the right way. As you said random results are common if you don't focus on your intent when you go into the experience. When it's coming from someone who puts a loving healing vibe into it and they are genuine caring people, more than 9 times out 10 that's exactly what you will get.