Can I trust all the Bible teachers I hear?
No! The Bible clearly and repeatedly warns that there will be false teachers. Some of them will come from outside the church. Jesus said to "beware of the false prophets, who come to you in sheep's clothing, but inwardly are ravenous wolves." (Matthew 7:15) And Paul warned that "savage wolves will come in among you, not sparing the flock" (Acts 20:29). Although we'd like to give everyone the benefit of the doubt and assume that all Bible teachers are well intentioned, Scripture says that "Satan disguises himself as an angel of light" and "his servants also disguise themselves as servants of righteousness" (2 Corinthians 11:14,15).

Some false teachers will even come from within the church. Paul warned the Ephesian church elders that "from among your own selves men will arise, speaking perverse things, to draw away the disciples after them. Therefore be on the alert." (Acts 20:30,31) Paul's first letter to Timothy describes men in church ministry who would want to be teachers "even though they do not understand either what they are saying or the matters about which they make confident assertions" (1 Timothy 1:7). And he wrote to Titus that "there are many rebellious men, empty talkers and deceivers, ... who must be silenced because they are upsetting whole families, teaching things they should not teach for the sake of sordid gain" (Titus 1:10,11).

God's word clearly warns us against naively believing every religious teacher, no matter how sincere or committed to the Bible he may seem.

How can I know if a Bible teacher is a false teacher?
The Bible warns us that there are many false teachers and commands us to turn from them.  In Matthew 7:15-20, a strongly worded passage, Jesus Himself warns against false prophets and tells how to identify them.

Twice He stressed that we will know false teachers by their fruits (Matthew 7:16, 20). To apply this test, we must examine the life of the teacher as well as the fruits that his teaching produces in his followers. Jesus assured us that, without exception, bad trees produce bad fruit and good trees produce good fruit.

Bad fruit would be a life characterized by the deeds of the flesh mentioned in Galatians 5:19-21: "immorality, impurity, sensuality, idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions, envying, drunkenness, carousing, and things like these."

Good fruit would be lives characterized by the nine-fold fruit of the Spirit listed in Galatians 5:22, 23: love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control.

Jesus said you can tell a false teacher from a faithful teacher by his fruit.  If God's Spirit and God's truth are the guiding factors in the ministry of a teacher, the fruit of the Spirit will be evident in the lives of that teacher and his followers.