The phenomenon known as Ayahuasca tourism has changed the landscape when it comes to finding a legitimate shaman. Ayahuasca is a sacred plant imbued with a living spirit. It should be revered, but it is frequently profaned.
Oftentimes deceitful individuals, pretending to be shamans, or brujos (shamans that use dark powers to inflict harm) will entice individuals into ceremony, principally for monetary gain. The threat is greater for women as they also risk sexual molestation. As well, there are many shamans, primarily driven by ego or greed, who will not likely take your best interests to heart.
It is essential you follow your intuition as failing to do so is like ignoring advice from spirit. Any shaman who tells you otherwise is at cross purposes with spirit.