Christians often decide that since their own group is correct, they should not listen to other groups. While there is some wisdom in this, there are also problems. I believe heavily in soul-winning and witnessing. What do I do if someone from another group is winning large numbers of souls, and he wants to offer me advice?
In Mark 9:40, Jesus said "For he who is not against us is on our side." Someone who couldn't get along with the apostles had been casting out demons in Jesus's Name, and the apostles had forbidden him to do it. But Jesus claimed that man as one of His own. Following Jesus closely means that you can get along with other Christians. It doesn't mean that you refuse to fellowship with, or have anything to do with them, because you think that your group is right.