Although there are those who intentionally deceive and have corrupt hearts, others are simply misguided.
Some will fake healings and miracles; others are just presumptuous.
In John 5:1-15, notice that Jesus goes to a place that is filled with disabled people, but doesn't heal everyone... He only heals ONE MAN, and then slips away into the crowd. (That's not the only time that crowds are looking for Jesus, but He deliberately remains low profile...)
When I hear people give blanket statements like, "You are healed!" to a big crowd, there are only two options: either they are intentionally deceitful, or just deceived themselves. Don't get me wrong, I believe in divine healing and miracles. I have been divinely healed more than once myself (including my mind and my body). However, everything God does is for His glory and according to His purpose. It's not like you can just claim anything for your own comfort or pleasure... Moreover, often we in the West are just plain full of ourselves, and God uses illness to humble us and teach us His way. Being stripped of our health may be the greatest blessing God could give us! It may just lead to true healing of the heart and soul!
I saw a man give a message to a big crowd, but then, it seemed like he wasn't satisfied with leaving the stage without something more... So, he said that he felt God wanted to heal the people in the crowd. So, after stirring them up, he asked them to lift up their hands if they felt they had been healed. Of course, a bunch of people did so, probably by the enthusiasm of the moment. However, in time, many of these people will find out that their illness or injury is still lingering... perhaps even worse now that they were careless for a period. Is it because they lack faith? No. It's just because God wasn't in this.
So, what is the point? The best remedy is a thorough knowledge of the Scriptures, spiritual discernment, and a genuine submission to the will of God. That way, people will not be deceived by the wolves, or misguided by those who don't know any better.
Praise God for His patience towards His children! Those sheep that are truly His own, He will make sure that they are looked after. (John 10) Otherwise, we would be dead meat already.
In Christ Jesus,
Renoncer