How shall we treat false teachers when they arise?

1.  So soon as we know their character, it is our duty to refuse to hear them or read their books.
2. If a false teacher is already in an orthodox Church, it is right to disown him, and cast him out, not with maledictions, but with sorrow and prayer and firmness.
3. False teachers must also be firmly and meekly resisted in all their attempts to lead men astray.
4. While the Scriptures call on us to feed the hungry and to be kind to the poor, they forbid us to hold such social intercourse with false teaches, as implies sympathy with them or connivance at their wicked teachings. ... We should not show them those hospitalities, which the churches usually extend to Christ's ministers.
5. In dealing with corrupt teachers, it is peculiarly important not to be intimidated by them.

From False Doctrines and Teachers: How to Know Them and How to Treat Them by William S. Plumer (1802-1880), pp.12-14, found in THE CHRISTIAN: To Which Is Added: FALSE DOCTRINES AND FALSE TEACHERS: How to Know Them, and How to Treat Them and ASSURANCE OF GRACE AND SALVATION: What it Is; How to Attain It; Why More Do Not Enjoy It and BALM FOR THE WOUNDED SPIRITS, Sprinkle Publications, 1997.