I will throw a few comments out.
I personally think it requires the Holy Spirit to make the decision on how to approach a particular person, and you need to consider whether they are trying to mislead others. If they are trying to mislead others, it calls for a much sterner approach. Also, if they don't claim to be Christians, perhaps the approach should be more gentler than if they are claiming to be a brother but are teaching false things. The reason is that they may be trying to influence others, and you need to nip that in the bud.
A big issue is being spiritually prepared. It is much easier to be excessively confrontational if you have been neglecting your spiritual life. That's generally where I've made my mistake. If I am not in tune with the Holy Spirit, I can become excessively confrontational.