Q. My neighbor is not shomer mitzvos, but I make a point to always great him warmly. Then when he drives his car on Shabbos (going to his shul), he makes a point if he sees me walking by, to open his window and say loudly Good Shabbos! Do I have to answer him? Should I be concerned that my not answering may be pushing him away from becoming a baal teshuva? Or maybe my greeting him back shows openly that Shabbos is not that important to me, and that is a great chilul Hashem. What is Horam Miller’s opinion?

A. Horav Shlomo Miller’s Shlit’a opinion is that you should not ignore him and simply and warmly say; Thank You.
The Rov added that you may try to invite him for a Shabbos meal, to be mekarev him.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a