Mark 6:12 So they went out and preached that people should repent.
It's hard to believe that an unsaved person can be a soul-winner, but it is possible. A major problem today with soul-winners is "easy believism." Easy believism is the doctrine that if you say "Jesus please save me," and mean it, you are saved, whether or not you believe the Gospel.
The Greek word translated "believe" has no perfect English translation. It does NOT mean that you believe that Jesus exists. The word means "completely accept, completely rely on, completely trust." A person who asks Jesus to save him, but has no intention of allowing Jesus to be Lord of his life, has not completely accepted Jesus. Nowhere in the Bible was a person saved by repeating a prayer, but many people in the Bible got saved by believing on the Lord Jesus Christ.
When a person turns to Christ, he has to turn AWAY from something at the same time. "Repentance" describes that turning away from sin. Getting large numbers of people to pray for salvation takes hard work and a lot of ability. Getting people to repent and believe the Gospel takes the power of God.
People who preach and teach easy believism do get people saved, but most of their numbers are false professions. (But to be fair, they are usually getting more genuine conversions that their critics are). Scripture plainly teaches that those who accept Christ will have changed lives, the indwelling Holy Spirit, a new birth, etc., and a person who merely prays for Jesus to save him, without repenting, does not have these things.