If you saw a person go into a restaurant on Shabbos who you knew was the owner and turned on the light
Later a friend asked you if that resturant was Kosher, would you tell them what you saw or not
Now lets say you were at the same restaurant and you saw roaches on the wall and a friend asked you what you thought of the restaurant.
Is it OK to tell people about the Mechalel Shabbos but not about the Roaches