The solution to this is simple: "Watch yourselves" (Luke 17:3). When we keep our emphasis on ourselves, we will pay attention to our own lives, how we live, and what particular sins we commit. Then we will be able to seek the Lord and improve ourselves, not someone else.
Later in this same passage Jesus teaches a method of watching yourself--do your duty. He teaches this through a parable where he takes the example of a servant to point out that when that servant has completed a day of serving, he deserves no special honor; he has simply done his duty. This is an example to us to serve and to keep our emphasis on serving with humility. We do not serve to show ourselves better than others and we do not serve to gain a greater standing for ourselves; rather, we serve because, in Christ, we are servants.
By serving in this way--by doing our duty--we will not become a cause for sin for someone else because we will be too busy following the Lord in our own lives to criticize them and lead them astray. In fact, we will more likely become a source of grace for them and an example, leading them closer to the Lord.