In his book "Precious remedies against Satan's devices" puritan Thomas Brooks lists seven characteristics of false teachers. They are:
1. False teachers are men pleasers.
2. False teachers are notable in casting dirt, scorn, and reproach upon the persons, names, and credits of Christ's most faithful ambassdors.
3. False teachers are venters of the devices and vision of their own heads and hearts.
4. False teachers easily pass over the great and weighty things both of law and gospel, and stand upon those things that are of the least importance and concern to the souls of men.
5. False teachers cover and color their dangerous principles and soul-deceptions with very fair speeches and plausible pretenses, with high notions and golden expressions.
6. False teachers strive more to win over men to their opinions, than to better them in their lives.
7. False teachers make mechandise of their followers.
And I would add to point seven, they make merchandise of God as well. Brooks wrote this in the 1600's, this could easily have been written today. This is a great book and on kindle it's dirt cheap, I highly recommend picking up a copy and adding it to your library.