How to treat a fellow Christian who prove to be an unrepentant wrongdoer like a tax collector?

The Bible says: “Stop keeping company with anyone called a brother who is sexually immoral or a greedy person or an idolater or a reviler or a drunkard or an extortioner, not even eating with such a man.” (1 Corinthians 5:11) Regarding everyone who “does not remain in the teaching of the Christ,” we read: “Do not receive him into your homes or say a greeting to him. For the one who says a greeting to him is a sharer in his wicked works.” (2 John 9-11). Strict avoidance is necessary first, it is a matter of loyalty to God and his Word. Second, withdrawing from an unrepentant wrongdoer protects us and the rest of the congregation from spiritual and moral contamination and upholds the congregation’s good name.

Did you have a question?

speak with your pastor if u really feel its your business which it is not

Jesus made tax collectors into disciples. You should do the same. That's the who point. You don't go to the emergency room in perfect health, you go when you have an emergency medical problem. If someone is an independent sinner and comes to you for help, you help them. You teach them, so they can become repentant.

Withdraw yourself from those who walk disorderly. See 2 Thessalonians 3:6. (in other words, avoid them)

Ostracizing was the normal practice then. Basically you ignore them, as if they did not exist.

A tax collector is a person that you do business with for the purpose of paying your bill and paying your taxes when they send you a bill you responded to them respectfully you do not lie to them you do not shun them but for the most part you do not seek them out!

The rules to this one are very simple you speak to them respectfully and truthfully when they seek you out but for the most part you do not seek them out! Just you try to shun or disrespect the tax collector and see how fast you wind up in front of the judge!

Treat him like the heathen man and a tax collector, continue to call him to repentant...

You treat them like you would your neighbor. Not rude, but not close like a brother about church matters.

Yep. Shake the dust off your feet and roll on.