Rav Nahman of Breslov has in one section of the LeM vol II ch 8 that one ought to seek after a true tzadik. While I can see the point of this, but the problems are the straight forward frauds which are the vast majority. And the people that imagine to themselves that they a have "Ruach Hakodesh" so they are not willfully defrauding others, but are close to that. Then there is the most insidious category of people the Sitra achra (dark side) gives miracles to and reveals things in to to gain acceptance and to be able to trick people after gaining their trust.

Can you by these facts deny the validity of all faith healers? I do not think so. 

Rather what I think is this. That one ought not to go after tzadikim. If one merits to it, the tzadik will come to you. but if you go around searching for one, it is 99.9% guaranteed you will find (and be funding) a phony;--  or even worse, perhaps agent of the Dark Side.

I think there is one true tzadik or one true faith healer among thousands of frauds. The best thing is to seek to serve God by by Torah and prayer and good deeds. Then if one merits to be close to a true tzadik then that will  happen.