Most 'evidence' for these people consists of vague testimonials for cases where there was either no proof that the person was ill before-hand, or diseases that can simply go in to remission.
Faith healers prey on the desperate and in some cases can actually cause deaths when people abandon conventional medicine because they have faith in the faith healer.
Steve: How do you know she had cancer in the first place or is actually cured?
John: Peter said she was cured.
Steve: Don't you think it odd that he never heals visible disorders like burns, scars or missing limbs? He only ever heals things that can't easily be seen. Why doesn't God want these people to be healed?