I'm very sorry if the questionable behavior of a few has turned you against God. The Bible's standard is clear, not just for those who are called to be evangelists, but also for all believers: "Walk before me faithfully with integrity of heart and uprightness" (1 Kings 9:4).
But I can't help but wonder if this is your real problem -- or if you're only using it as an excuse to keep God out of your life. Do you refuse to consult a lawyer just because a few aren't honest? Do you refuse to visit a restaurant just because a few aren't clean? Do you refuse to get on an airplane because one occasionally crashes? Neither should you turn your back on God because a few who claim to follow Him don't live up to their calling.
No Christian is perfect; we all need God's forgiveness and grace. But so do you, whether you admit it or not. This is why I urge you to look at Jesus Christ. He alone is perfect, and He alone can change our lives and give us hope for the future. The reason is because He was God in human flesh, sent from heaven to save us from our sins.
Don't let your pride, or your love of sin, or anything else keep you from facing your need for Christ. As I often say, don't gamble with your soul. The Bible says, "Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it" (Matthew 7:13).