10-11 Do not move an ancient landmark or enter the fields of the fatherless, for their  Redeemer is strong; he will plead their cause against you. 12 Apply your heart to instruction and your ear to words of knowledge.

13-14 Do not withhold discipline from a child; if you strike him with a rod, he will not die. If you strike him with the rod, you will save his soul from Sheol.

15-16 My son, if your heart is wise, my heart too will be glad. My inmost being will exult when your lips speak what is right. 17-18 Let not your heart envy sinners, but continue in the fear of the  Lord all the day. Surely there is a future, and your hope will not be cut off. Proverbs 23:10-18 (English Standard Version)

What sort of person would move landmarks (which in those days may have just been stones) to get more ground for themselves? And what sort of person exploits vulnerable widows, as pictured in vs 10-11? Could vs 12 be a clue to the sort of people who would do such evil things?

I'd suggest they would be people who didn't do what the father was urging his son to do in that verse. They never took instruction to heart, and they never listened to anyone who was trying to show them a wise way for living. Do you think vs 13-14 could also be a reason why some people end up with dishonest lifestyles, and exploit the vulnerable?

It's likely that some who end up doing wrong things are people whose parents never took the time and trouble to correct them as they grew, even with punishment when needed. Don't be side-tracked by the word 'rod'. The Bible isn't teaching that parents should beat a child in a dangerous way. But it is showing that (what we call) 'a spanking' will do the child a world of good rather than harm. As it says there, 'he won't die!' But look what it can save him from in the long run. 'Sheol' refers to beyond the grave and was pictured as a gloomy place. It's not unusual for those who choose to live lawless lives to meet an early end!

When it comes to correction, including strong discipline, it's helpful to keep in mind what a New Testament writer said. Much like this father in Proverbs, he wrote: “My son, don't regard lightly the discipline of the Lord, nor be weary when reproved by Him. The Lord disciplines the one He loves, and chastises every son whom He receives. We had earthly fathers who disciplined us - and we respected them. Shall we not much more be subject to the Father of spirits and live? They disciplined us for a short time as it seemed best to them, but He disciplines us for our good, that we may share His holiness. For the moment, all discipline seems painful rather than pleasant, but later it yields the peaceful fruit of righteousness to those who have been trained by it.” (Hebrews 12:5-6, 9-12)

Some of the trials we go through as Christians can be God's loving correction and discipline. And without such correction we could shipwreck our faith. What is a parent's response when a child does listen, and follows what is good and right? (vs 15-16)

Their hearts are gladdened and they rejoice to the depths of their being! The amazing thing is that our heavenly Father's heart is made glad too. In Jeremiah 9:24 we read “I am the Lord who practises steadfast love, justice, and righteousness in the earth. For in these things I delight, declares the Lord.”

Verses 17-18 fit in well with all the above. The father urges his son to not be envious of those who get rich through sinful means (like moving landmarks and exploiting widows), but to rather fear God, and keep to what is good and right. He says that will lead to a hope and a future. That includes a hope and a future beyond Sheol. Jesus spoke of the resurrection of the righteous, to whom the kingdom of heaven belongs.