The story about giving someone money for kosher food so they won’t eat at MacDonalds (but not knowing if in fact they would use the money for kosher food) , reminded me of something that happened with me a long time ago. I was the shomeres for a kallah on her Shabbos kallah, and she was heavily into kiruv and invited a non-frum single co-worker to spend the shabbos as well. She wanteed her to see how enjoyable Shabbos could be and how much fun we would have being that it was an extra-special Shabbos.
When we were ready to turn in, we each had our own bedrooms, and I noticed that the girl had turned her light on. Gaivedig big shot that I was, I decided to prevent her from being further mechallel shabbos by turning her light off, so I offered her my (dark) room so she would have no need to turn off a light. I didn’t tell her my reasoning (that was a mistake, btw, as I should have told her that we don’t turn the lights on and off on Shabbos). She was puzzled, but switched rooms with me, and then promptly turned THAT room’s light on. Meanwhile, I had to sleep in a well-lit (and as it turned out, extremely freezing cold) room. Didn’t get much sleep that night, but consoled myself with the fact that I had tried to help someone from doing an aveira. Talk about personal hubris!