When understanding where someone else is at, I always try and work from this passage:
Matthew 7:13-16 HCSB
Enter through the narrow gate. For the gate is wide and the road is broad that leads to destruction, and there are many who go through it. How narrow is the gate and difficult the road that leads to life, and few find it. Beware of false prophets who come to you in sheep's clothing but inwardly are ravaging wolves. You'll recognize them by their fruit. Are grapes gathered from thornbushes or figs from thistles?
As v13-14 let us in on, it's difficult. This means that just as God gave us grace, we are to give grace to others. It's too easy to let one mistake write someone off. If the Bible says that the way is difficult, the way is difficult. That means both for us and for them. There will be stumbles and bad days.
The second part of that is that you'll know a person by their fruit - what they produce. A lot of people like to focus in on Matthew 7:18 which says a good tree cannot produce bad fruit. Unfortunately, I think overemphasizing that verse and de-emphasizing Matthew 7:13-14 will result in skewed understanding. Yes, a good tree will not produce consistently bad fruit. However, we produce fruit because of Christ, and in general even a Christian who screws up still has other evidence of God being at work in his or her life.
This passage is primarily directed at false apostles, but nonetheless applies to any relationship in Christ.