From the tone of your question, I can see that you are quite skeptical of the claims of modern spiritual faith healers. I am as well. The question is, how should we treat people who do these sorts of things and, more importantly, those influenced by these "healing" ministries?
I believe the first principle here is humility and the second principle is correct doctrine. I say this because it is a disputable matter. I assume that you will agree that God can perform miraculous healings if he so desires. I would guess that you also believe that at times he does in fact move in a way which causes people to be miraculously healed. Even if you do not agree that this does happen, it is not a ridiculous or heretical thought that God does heal people today. I believe we should be a bit cautious about how we spread our skepticism around. Personally, I believe that the vast majority of these "healings" in these churches are not in fact miraculous healings, but are subjective or even placebo-effect events. Many of these healings are being done by people who are not even baptized disciples of Jesus and are therefore not Christians. I am extremely skeptical of these healing ministries. They tend to focus attention on the supposed healers rather than the real healer, which is Jesus Christ. They tend to produce a personality cult (but certainly not in every case).
Having said that, and given that God can and probably does heal people, I believe our stance ought to be to not directly confront or attack belief in these healings. Generally, I tend to deflect the discussion from these debatable matters to more important matters such as salvation, sin, redemption and personal holiness. It is probably much more likely that you will come across a person influenced by one of these ministries than the healer his/herself. I would not try to prove theire belief wrong. Such experiences are highly subjective and experiential. They tend to not be affected by logical arguments. Given that logical arguments are not likely to change the perception, I try to move their focus to Jesus, to the kingdom of God and to righteousness. When people realize that they are lost, their attention to whether or not so and so worked a miraculous healing is greatly reduced. Then, later on, they will be open to considering the possibility that their experience may have been misinterpreted as a miracle (or maybe not. who knows….).