Never forget: For all the little bit of positive results for a placebo there are also negative effects due to noceboeffect. Also it's very common in esoterica that if it works it was the healer if it didn't it was something you did wrong.
People in traditional cultures are inclined to believe that there is an evil influence involved whenever anything goes wrong. If you're in a culture like that and people believe you can throw curses, you can get material benefit through the threat of throwing curses or make a living throwing curses.
When people were [1] prosecuted for "practicing witchcraft" courts record testimony that promises were made, payments were made, all of that.
Effective curses are not an application of psi (you zapped someone with telepathy) or an evocation of evil spirits, but are loud, noisy, public and supported by the whole social environment, see
https://en.wikipedia.org/wiki/Voodoo_death
I can't say that any magic-user today should practice that sort of stuff, there is the "it gets returned you (3|10) times" bit and that you don't have the social support that the African "witch doctor", Chinese fox medium, Navajo skin-walker, or Italian Nonna who casts the "evil eye". But if you're looking for a social-scientific explanation of how magic works it is a dramatic example.
[1] and still are in some places